Magnetic disk device and method of manufacturing same

ABSTRACT

A magnetic disk drive device that includes a disk-shaped medium with a magnetic film formed on a surface for recording or reproducing information, and a magnetic head for recording on and reproducing information from the disk-shaped medium. The disk-shaped medium has a data recording region and a control signal recording region. The data recording region is impressed to have convex recording regions for recording data and concave guard bands for separating adjacent recording regions. The control signal recording region has impressed concavities and convexities representing tracking marks (for effecting tracking control of the magnetic head), track number indicating marks and track numbers (for identifying the tracks), and clock marks dividing one circumference into equal intervals along a path of angular movement of the magnetic head. The disk-shaped medium has reduced track pitch and increased recording capacity because the concave guard bands can be very narrow without inducing crosstalk, and the tracking marks, track number indicating marks, and clock marks are impressed as concavities and convexities along the path of angular movement of the magnetic head.

This is a continuation of application Ser. No. 08/704,435, filed Aug.26, 1996, U.S. Pat. No. 5,907,448 which is a continuation of applicationSer. No. 08/331,588 filed on Dec. 12, 1994, now abandoned.

TECHNICAL FIELD

The present invention relates to a magnetic disk device suitable for useas a hard disk drive in a computer system, for example, and a method ofmanufacturing such a magnetic disk device.

BACKGROUND ART

Computer systems employ hard disk devices and can quickly accessprograms or data recorded in the hard disk devices. In such a hard diskdevice, a magnetic film is formed on each of the surfaces of a magneticdisk, and data are recorded on and reproduced from the magnetic film bya flying-type magnetic head. The hard disk device comprises a mechanismfor actuating the magnetic head and a drive unit for driving themagnetic disk, the mechanism and the drive unit being assembled in acasing. The hard disk device can record data on the magnetic disk at arelatively high density.

The magnetic film is formed on the entire surfaces of the magnetic diskin the conventional magnetic disk device. Therefore, it has beennecessary to provide guard bands of relatively large width betweentracks in order to suppress crosstalk from adjacent tracks. As a result,a track pitch cannot be reduced, presenting an obstacle to efforts torealize a small-size device having a large recording capacity.

If an encoder clock signal is recorded in advance on a magnetic disk andthereafter the magnetic disk is assembled in a casing, then anattachment error (eccentricity) tends to occur in the assemblingprocess, making it difficult to record and reproduced data in and froman exact position on the magnetic disk. Heretofore, it has beencustomary to assemble a magnetic disk in a casing, and thereafter recordan encoder signal on the magnetic disk. As a consequence, it has beentime-consuming and costly to complete the device.

The present invention has been made in view of the above drawbacks, andprovides a magnetic disk device which is of a low cost and has ahigher-density recording capacity, and a method of manufacturing such amagnetic disk device.

DISCLOSURE OF THE INVENTION

A magnetic disk device of the present invention has a disk-shaped medium(magnetic disk) with a magnetic film formed on a surface for recordingor reproducing information, a magnetic head (recording head and playbackhead) for recording on and reproducing information from said disk-shapedmedium, an arm supporting said magnetic head and angularly movable tomove said magnetic head to a predetermined radial position on saiddisk-shaped medium, characterized in that said disk-shaped medium has adata recording region and a control signal recording region (servo datarecording region and ID recording region, said data recording region hasconcentric or spiral tracks formed therein, said tracks being impressedto have convexities as recording portions for recording data andconcavities as guard bands for separating adjacent ones of saidrecording portions, said control signal recording region havingimpressed concavities and convexities representing tracking marks(wobbled marks for effecting tracking control on said magnetic head,track number indicating marks (gray code and track numbers) foridentifying said tracks, and clock marks dividing one circumference intoequal intervals, at least one of the marks being formed along a path ofangular movement of said magnetic head, the arrangement being such thatrecording or reproducing operation of said magnetic head is controlledaccording to a signal produced by reproducing said tracking marks, saidtrack number indicating marks, or said clock marks.

In another aspect of the present invention, the magnetic disk device hasa disk-shaped medium (magnetic disks) with a magnetic film formed on asurface for recording or reproducing information, a magnetic head forrecording on and reproducing information from said disk-shaped medium,characterized in that said disk-shaped medium has a data recordingregion and a control signal recording region (servo data recordingregion and ID recording region), said data recording region hasconcentric or spiral tracks formed therein, said tracks being impressedto have convexities as recording portions for recording data andconcavities as guard bands for separating adjacent ones of saidrecording portions, said control signal recording region havingimpressed concavities and convexities representing at least trackingmarks (wobbled marks) for effecting tracking control on said magnetichead, track number indicating marks (gray code and track numbers foridentifying said tracks, and clock marks dividing one circumference intoequal intervals, the arrangement being such that said magnetic headmeasures a change corresponding to eccentricity of said disk-shapedmedium from a signal produced by reproducing said tracking marks, saidtrack number indicating marks, or said clock marks, and recording orreproducing operation of said magnetic head is controlled according to aresult of measurement.

The tracking marks, said track number indicating marks, and said clockmarks may be provided in 1000 combinations or less per circumference.The control signal recording region may occupy 40% or less of onecircumference of said disk-shaped medium, The disk-shaped medium maycomprise a resin or glass substrate, for example.

The magnetic head may be separated into a recording head for recordingdata, and a playback head for reproducing data.

The tracking marks and said track number indicating marks may have firstmarks used when data are recorded and second marks used when data arereproduced, said second marks being disposed along substantial centersof said tracks, and said first marks being disposed at positions thatare displaced a predetermined distance radially from substantial centersof said tracks. The tracking marks and said track number indicatingmarks may comprise a plurality of marks having the same function.

A change corresponding to eccentricity of said disk-shaped medium may bea positional change measured from said tracking marks or said tracknumber indicating marks, or a time change measured from said clockmarks.

An eccentricity control quantity for correcting a positional deviationdue to eccentricity of said magnetic head from said tracks may becalculated from the signal produced by reproducing said tracking marks,said track number indicating marks, or said clock marks. Theeccentricity control quantity which is calculated may be stored, and thestored eccentricity control quantity may be read out and added to atracking control signal to effect tracking control on said magnetichead. Alternatively, a clock signal may be generated in synchronism withsaid clock marks, the time change measured from said clock marks may bestored, and a time base of said clock signal may be corrected accordingto the stored time change.

The signal produced by reproducing said track number indicating marksmay be subjected to CRC calculations simultaneously while the signal isbeing Viterbi-decoded.

A clock signal may be generated from the signal produced by reproducingsaid clock marks, recording data may be delayed according to said clocksignal, and the delayed recording data may be recorded on saiddisk-shaped medium.

The magnitude of a relative positional deviation between said magnetichead and said tracks as measured from said tracking marks may bedetermined, and recording operation on said disk-shaped medium may becontrolled according to a result of determination.

A casing which houses the disk-shaped medium and the magnetic head mayhave only a vent hole.

The disk-shaped medium may have a diameter of about 2.5, 1.8, or 1.3inches.

A method of manufacturing a magnetic disk device having a disk-shapedmedium with a magnetic film formed on a surface for recording orreproducing information, and a magnetic head for recording on andreproducing information from said disk-shaped medium is characterized bythe steps of forming a data recording region and a control signalrecording region (servo data recording region) on said disk-shapedmedium, forming concentric or spiral tracks in said data recordingregion, said tracks being impressed to have convexities as recordingportions for recording data and concavities as guard bands forseparating adjacent ones of said recording portions, forming impressedconcavities and convexities in said control signal recording regionwhich represent at least tracking marks (wobbled marks) for effectingtracking control on said magnetic head, track number indicating marks(gray code and track numbers) for identifying said tracks, and clockmarks dividing one circumference into equal intervals, and assemblingsaid disk-shaped medium and said magnetic head in a casing after saidtracking marks, said track number indicating marks, and said clock markshave been formed and recorded on the disk-shaped medium.

The guard bands are formed as physical concavities with respect to therecording portions in which data are recorded in the tracks. Therefore,no data are reproduced from the guard bands, the guard bands are notrequired to be wide for reducing crosstalk. It is possible to narrow theguard bands, and increase the recording capacity.

The tracking marks, the track number indicating marks, or the clockmarks are impressed as concavities and convexities along the path ofangular movement of the magnetic head. Therefore, these marks can bearranged highly accurately in desired positions by using opticaltechnology, for example. Even if the track pitch is reduced, data canaccurately be recorded and reproduced.

In the magnetic disk device of the present invention, eccentricity ofthe disk-shaped medium is measured, and recording or reproducingoperation is controlled according to the measured eccentricity.Therefore, the magnetic head can accurately access the tracks regardlessof eccentricity produced due to an attachment error at the time themagnetic disk is assembled even though the disk-shaped medium on whichthe tracking marks, the track number indicating marks, and the clockmarks are recorded in advance is assembled into the casing.

In the method of manufacturing a magnetic disk device of the presentinvention, the disk-shaped medium is assembled in the casing after thetracking marks, the track number indicating marks, and the clock markshave been impressed in concavities and convexities on the disk-shapedmedium. As a consequence, after the disk-shaped medium has beenassembled, any process of recording an encoder thereon is not required,and the magnetic disk device can be completed quickly. As a result, thecost of the magnetic disk device can be lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an entire arrangement of a magnetic diskdevice according to the present invention;

FIG. 2 is a diagram showing formats of a servo data recording region anda data recording region of a magnetic disk according to the presentinvention;

FIG. 3 is a diagram showing a format of a servo data recording region inwhich a unique pattern exists, of the magnetic disk according to thepresent invention;

FIG. 4 is a diagram showing a format of a servo data recording region inwhich a home index exists, of the magnetic disk according to the presentinvention;

FIG. 5 is a diagram showing a format of a servo data recording region inwhich no unique pattern and no home index exist, of the magnetic diskaccording to the present invention;

FIG. 6 is a view showing the relationship between servo data recordingregions and data recording regions of a magnetic disk according to thepresent invention, and the path of angular movement of a magnetic head;

FIG. 7 is a diagram showing a planar configuration of the servo datarecording region of the magnetic disk according to the presentinvention;

FIGS. 8A and 8B are cross-sectional views of the magnetic disk accordingto the present invention;

FIG. 9 is a view of an impressed pattern of convexities and concavitieson the magnetic disk according to the present invention;

FIGS. 10A and 10B are views illustrating a process of magnetizing themagnetic disk with convexities and concavities according to the presentinvention;

FIG. 11 is a cross-sectional view of a more detailed sectional structureof the magnetic disk according to the present invention;

FIG. 12 is a plan view which schematically illustrates the servo datarecording region and the data recording region of the magnetic diskaccording to the present invention;

FIG. 13 is a view showing the relationship between a slider according tothe present invention and the magnetic disk;

FIG. 14 is a diagram illustrative of a change in the amount of floatingof the slider in the vicinity of a concavity on the magnetic disk;

FIG. 15 is a diagram showing the proportions of the servo data recordingregion and the data recording region, which are used in the simulationof a change in the amount of floating of the slider;

FIG. 16 is a diagram showing the manner in which the amount of floatingof the slider varies in a segment period according to the presentinvention;

FIG. 17 is a front elevational view of the magnetic head according tothe present invention;

FIG. 18 is a cross-sectional view of the magnetic head according to thepresent invention;

FIG. 19 is a perspective view showing an arm according to the presentinvention;

FIG. 20 is a cross-sectional view of a ball bearing shown in FIG. 19;

FIG. 21 is a block diagram of a circuit for correcting a time base errorof a clock signal according to the present invention;

FIG. 22 is a diagram illustrative of an operation of eccentricity;

FIG. 23 is a diagram showing the manner in which the phase of a PLLclock varies with respect to a disk clock;

FIG. 24 is a block diagram of another circuit for correcting a time baseerror of a clock signal according to the present invention;

FIG. 25 is a diagram showing the relationship between clock marks andeccentricity;

FIG. 26 is a block diagram of an arrangement of an eccentricitymeasuring unit 50-25 shown in FIG. 21;

FIG. 27 is a diagram illustrating time intervals of a reproduced clockmark signal;

FIG. 28 is a diagram showing the manner in which a clock time intervalcount varies;

FIG. 29 is a diagram illustrative of the amount of eccentricity;

FIG. 30 is a block diagram of another arrangement of the eccentricitymeasuring unit 50-25;

FIG. 31 is a diagram illustrating time intervals of a reproduced clockmark signal in the embodiment shown in FIG. 30;

FIG. 32 is a diagram showing the manner in which a clock time intervalvaries in the embodiment shown in FIG. 30;

FIG. 33 is a diagram illustrative of the amount of eccentricity in theembodiment shown in FIG. 30;

FIG. 34 is a block diagram of a tracking servo circuit according to thepresent invention;

FIG. 35 is a diagram illustrating transfer characteristics of theembodiment shown in FIG. 34;

FIG. 36 is a diagram illustrating a disturbance suppression gain of aclosed loop in the embodiment shown in FIG. 34;

FIG. 37 is a diagram illustrating an apparent disturbance suppressiongain in the embodiment shown in FIG. 34;

FIG. 38 is a block diagram of a circuit for determining an off-trackcondition according to the present invention;

FIG. 39 is a flowchart of an operation sequence of the embodiment shownin FIG. 38;

FIGS. 40A and 40B are diagrams showing response waveforms produced whena shock or 10 G or 100 G is applied;

FIG. 41 is a diagram showing a response waveform produced immediatelyafter a shock of 100 G is applied;

FIG. 42 is a diagram showing the path of movement of a head at the timea shock of 100 G is applied;

FIG. 43 is a diagram showing a response waveform produced when a shockof 100 G and noise are applied;

FIGS. 44A, 44B, and 44C are diagrams illustrative of the states of pathsin Viterbi decoding;

FIG. 45 is a block diagram of a Viterbi decoding circuit;

FIG. 46 is a timing chart illustrative of operation of the embodimentshown in FIG. 45;

FIG. 47 is a block diagram of a RAM 80-18 shown in FIG. 45;

FIGS. 48A and 48B are timing charts illustrative of operation of theembodiment shown in FIG. 47;

FIG. 49 is a block diagram of a circuit for simultaneously effectingViterbi decoding and CRC calculations;

FIGS. 50A and 50B are timing charts illustrative of operation of theembodiment shown in FIG. 49;

FIG. 51 is a block diagram of a recording circuit according to thepresent invention;

FIGS. 52A˜52H are timing charts illustrative of operation of theembodiment shown in FIG. 51;

FIG. 53 is a block diagram of an arrangement of a delay time controlcircuit 90-20 shown in FIG. 51;

FIG. 54 is a block diagram of a pulse delay circuit 90-30 shown in FIG.51;

FIG. 55 is a block diagram of another arrangement of the delay timecontrol circuit 90-20 shown in FIG. 51;

FIG. 56 is a view showing a recording format of a magnetic disk to whichthe present invention is applied;

FIG. 57 is a block diagram of a recording circuit according to thepresent invention which incorporates the embodiment shown in FIG. 56;

FIGS. 58A, 58B, and 58C are timing charts illustrative of operation ofthe embodiment shown in FIG. 57;

FIG. 59 is an exploded perspective view showing how a casing andinternal parts according to the present invention are assembled;

FIG. 60 is a perspective view of the casing according to the presentinvention;

FIG. 61 is a cross-sectional view of the embodiment shown in FIG. 60;

FIG. 62 is a perspective view of another embodiment of the casingaccording to the present invention;

FIG. 63 is a cross-sectional view of the embodiment shown in FIG. 62;

FIG. 64 is a table of changes in the amount of floating of the slider atthe time it moves over the servo data recording region, with the ratioof the servo data recording region to the data recording region persegment being as a parameter;

FIG. 65 is a table of input conditions, condition patterns, updatingrules, and output data when β=1;

FIG. 66 is a table of input conditions, condition patterns, updatingrules, and output data when β=1; and

FIG. 67 is a perspective view of a conventional casing.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows an entire arrangement of a magnetic disk device accordingto the present invention. A motor 10-1 rotates a magnetic disk 10-2 at apredetermined speed. A recording head 10-3 and a playback head 10-4 aremounted on an arm 10-5. The arm 10-5 is angularly movable about a shaftto move the recording head 10-3 and the playback head 10-4 to a radialposition over the magnetic disk 10-2. The motor 10-1, the magnetic disk10-2, the recording head 10-3, the playback head 10-4, and the arm 10-5are housed in a casing 1010.

The magnetic disk 10-2 has various marks. The playback head 10-4reproduces the marks and outputs a signal representing the reproducedmarks, from which a clock signal generator 10-6 generates and outputs aclock signal to a tracking servo unit 10-7 and a reproducer 10-8. Thetracking servo unit 10-7 refers to the clock signal supplied from theclock signal generator 10-6, generates a tracking error signal from thesignal outputted from the playback head 10-4, and actuates the arm 10-5based on the tracking error signal. The recording head 10-3 and theplayback head 10-4 are moved under tracking control to a radial positionover the magnetic disk 10-2.

A recorder 10-9 receives a recording signal supplied from a circuit (notshown), and causes the recording head 10-3 to record the recordingsignal on the magnetic disk 10-2. The playback head 10-4 reproduces datarecorded on the magnetic disk 10-2 and outputs a signal representing thereproduced data. The reproducer 10-8 demodulates the recorded data fromthe signal outputted from the playback head 10-4, and outputs thedemodulated data to a circuit (not shown),

The tracking servo unit 10-7 monitors the tracking error signal andcontrols the recorder 10-9 to stop recording operation when a largeshock is applied to the device to displace the recording head 10-3 offtrack.

The foregoing description is concerned with the overall arrangement andoperation of the magnetic disk device. The present invention is directedto many aspects in the magnetic disk device, and each of such aspectswill be described below.

First, an aspect relative to the magnetic disk 10-2 will be described. Aformat, a planar shape, a cross-sectional shape, a magnetizing process,a surface treatment, and the proportion of servo data regions of themagnetic disk will be described.

Then, an aspect with respect to the recording head 10-3 and the playbackhead 10-4 will be described with reference to FIGS. 17 and 18. A gap anda cross-sectional structure of a magnetic head will be described.

Thereafter, an aspect relative to the arm 10-5 will be described withreference to FIGS. 19 and 20. An arm structure will be described.

After the arm 10-5, an aspect relative to the clock signal generatorwill be described below with reference to FIGS. 21 through 33. Thegeneration of a clock signal, and a process of measuring eccentricityrequired for time base correction of the clock signal will be described.

Then, an aspect concerning the tracking servo unit 10-7 will bedescribed with reference to FIGS. 34 through 43. Tracking servooperation and the number of servo data recording regions necessary fortracking servo will be described below. A process of determining anoff-track condition using a tracking error signal will also bedescribed.

Furthermore, an aspect relative to the reproducer 10-8 will be describedwith reference to FIGS. 44 through 50, and an aspect relative to therecorder 10-9 will be described with reference to FIGS. 51 through 58.Reproduction and recording of data will be described.

Finally, an aspect regarding the casing 10-10 will be described withreference to FIGS. 59 through 64. The casing which houses the magnetichead, the magnetic disk, etc. will be described.

To describe each of the aspects in a manner suitable for them, thearrangement shown in FIG. 1 is divided into elements as required, andonly necessary elements are picked up and reconstructed. Therefore,technical elements used in the description of each aspect are not heldin one-to-one correspondence to the divided elements shown in FIG. 1.This is because only necessary technical elements are rejoined andexpressed in order to describe each technical aspect.

The aspect with respect to the magnetic disk 10-2 shown in FIG. 1 willfirst be described below.

The magnetic disk used in the magnetic disk device is circumferentiallydivided into 60 sectors each composed of 16 segments. Therefore, themagnetic disk is circumferentially composed of 840 segments. Eachsegment is divided into a servo data recording region and a datarecording region (20-40 and 20-41 in FIG. 2 or 21-2 and 21-3 shown inFIG. 6). Each servo data recording region has a gray code 20-71, a clockmark 20-11, and wobbled marks 20-12, 20-13. A unique pattern 20-72 isadded to the first segment of each sector. In one of the 60 sectors,however, a home index 20-73 having a function as PG is recorded insteadof the unique pattern.

FIG. 3 shows an arrangement of the servo data recording region 20-40 inwhich the unique pattern 20-72 is formed. The servo data recordingregion 20-40 includes the gray code 20-71 next to the unique pattern20-72, the clock mark 20-11 next to the gray code 20-71, and the wobbledmarks 20-12, 20-13 next to the clock mark 20-11.

FIG. 4 shows an arrangement of the servo data recording region 20-40 inwhich the home index 20-73 is disposed instead of the unique pattern20-72. FIG. 5 shows an example in which neither unique pattern 20-72 norhome index 20-73 is formed.

FIG. 2 shows the servo data recording region 20-40 in which the uniquepattern 20-72 is formed and the data recording region 20-41 immediatelyfollowing the servo data recording region 20-40.

In this embodiment, the unique pattern 20-72, the gray code 20-71(representing absolute addresses 0 through 2800 (track numbers)indicative of tracks), the clock mark 20-11, and the wobbled marks 20-12(20-12-1, 20-12-2), 20-13 (20-13-1, 20-13-2) are formed and recorded inthe servo data recording region 20-40.

If the width of the clock mark 20-11 in the direction of tracks (thewidth in the horizontal direction in FIG. 2) is 1, then the gray code20-71 has a width of 20 and the unique pattern 20-72 has a width of 16.

The clock mark 20-11 is a mark for generating a timing signal whichserves as a reference for recording and reproducing data. When aplayback head 20-30 reproduces the clock mark 20-11, the playback head20-30 outputs a timing signal corresponding to an edge of the clock mark20-11. As shown in FIG. 2, the clock mark 20-11 is formed not only indata tracks 20-10 but also in regions between tracks 20-10 (intertrackregions). Therefore, the clock mark 20-11 is formed continuouslyradially on the disk (see FIG. 6).

The wobbled marks 20-12-1, 20-13-1 are disposed radially outwardly andinwardly of a center line L1 of the tracks 20-10, and spaced a distancefrom each other in the direction of tracks. When the playback head 20-30reproduces the wobbled marks 20-12-1, 20-13-1, the playback head 20-30outputs positional pulses corresponding to edge positions of the wobbledmarks 20-12-1, 20-13-1. The playback head 20-30 can be positioned on thecenter line L1 of the tracks 20-10 by effecting tracking servo controlfor equalizing the levels of the positional pulses.

Other wobbled marks 20-12-2, 20-13-2 are also provided. These wobbledmarks 20-12-2, 20-13-2 will be described later on.

The wobbled marks 20-12-1, 20-13-1, 20-12-2, 20-13-2 have the same width(the length in the direction of tracks) as the clock mark 20-1, thewidth being 0.6 μm in the radially innermost position and 1.2 μm in theradially outermost position.

An ID recording region 20-41H is formed at the first area of the datarecording region 20-41. Data to be recorded and reproduced are recordedin a region 20-41D which follows the ID recording region 20-41H.

The ID recording region 20-41H is divided into a sector number recordingregion 20-41A and a track number recording region 20-41B (20-41-B1,20-41B2). At least the sector number recording region 20-41A is formedcontinuously radially between tracks as well as in the tracks 20-10. Asector number 20-41a indicative of a sector is recorded in the sectornumber recording region 20-41A. A track number 20-41b indicative of atrack is recorded in the track number recording region 20-41B. Theplayback head 20-30 outputs a pulse train when it reproduces the IDrecording region 20-41H.

Data of 40 bits composed of a sector number of 8 bits and two tracknumbers each of 16 bits are ID data recorded in the ID recording region20-41H.

These ID data are PR (partial response) (-1, 0, 1)-modulated, andrecorded in the ID recording region 20-41H.

If the magnetic disk is a CAV disk, then sector numbers are the same onradially inner and outer tracks. The sector numbers are recordedcontinuously in regions between tracks as well as in the tracks 20-10.

The track number recording region 20-41B is divided into a track numberrecording region 20-41B1 for playback operation and a track numberrecording region 20-41B2 for recording operation.

The track number recording region 20-41B1 for playback operation isformed such that its center (center in the direction of width) ispositioned on the center line L1 of the tracks 20-10. However, the tracknumber recording region 20-41B2 for recording operation is formed suchthat its center line L2 is spaced (offset) from the center line L1 ofthe tracks 20-10 by a distance d in a direction perpendicular to thetracks 20-10 (in the radial direction of the disk). Identical tracknumbers 20-41b1, 20-41b2 are recorded in the track number recordingregion 20-41B1 for playback operation and the track number recordingregion 20-41B2 for recording operation.

Two or more identical track numbers may be recorded in each of theregions 20-41B1, 20-41B2, so that track numbers can be read morereliably.

The offset distance d of the track number recording region 20-41B2 forrecording operation is progressive smaller in the radially inwarddirection and larger in the radially outward direction.

As shown in FIG. 2, the wobbled marks 20-12-1, 20-13-1 are formed forpositioning the playback head 20-30 with respect to the center line L1of the tracks 20-10 (in the sector number recording region 20-41A andthe track number recording region 20-41B1 for playback operation), andthe wobbled marks 20-12-2, 20-13-2 are formed in the servo datarecording region 20-40 for positioning the playback head 20-30 to tracethe center line L2 of the track number recording region 20-41B2 forrecording operation.

In a playback mode, therefore, the playback head 20-30 can be scannedalong the center line L1 of the tracks 20-10 by effecting trackingcontrol on the playback head 20-30 with respect to the wobbled marks20-12-1, 20-13-1.

In a recording mode, the playback head 20-30 can be scanned along thecenter line L2 of the track number recording region 20-41B2 forrecording operation by effecting tracking control based on a trackingerror signal that is produced when the wobbled marks 20-12-2, 20-13-2are reproduced by the playback head 20-30. At this time, a recordinghead 20-31 runs along the center line L1 of the tracks 20-10.

In the above embodiment, the ordinary wobbled marks 20-12-1, 20-13-1,the offset wobbled marks 20-12-2, 20-13-2, the sector number recordingregion 20-41A, the track number recording region 20-41B1 for playbackoperation, the track number recording region 20-41B2 for recordingoperation, and the region 20-41D are arranged in the order named.However, a second group of the offset wobbled marks 20-12-2, 20-13-2,the offset track number recording region 20-41B2 for recordingoperation, and the region 20-41D may be repeatedly arranged following afirst group of the ordinary wobbled marks 20-12-1, 20-13-1, the sectornumber recording region 20-41A, the track number recording region20-41B1 for playback operation, and the region 20-41D.

The track numbers 20-41b1, 20-41b2 recorded in the track numberrecording regions 20-41B1, 20-41B2 are used by a recording/reproducingsystem. The gray code 20-71 corresponds to the recording/reproducingsystem, but is used by a servo system. They are not identical to eachother. However, they are used in a control process for confirming tracksto record data therein or reproduce data therefrom. Therefore, the servorecording region 20-40 and the ID recording region 20-41H can berecognized as control signal recording regions.

Since regions for recording sector numbers or track numbers are formed,and sector numbers or track numbers are recorded in those regions, thesector numbers or track numbers can reliably be reproduced irrespectiveof how the playback head is positioned.

According to the present invention, servo data including the uniquepattern 20-72, the home index 20-73, the gray code 20-71, the clock mark20-11, the wobbled marks 20-12, 20-13 in the servo data recording region20-40, and the sector number 20-41a, the track numbers 20-41b1, 20-41bin the ID recording region 20-41H, and tracks are formed and recorded asconvexities and concavities (which are impressed).

For example, a guard band 20-20 is formed such that it is 200 nm lowerthan the data tracks 20-10 (as a concavity). Therefore, the tracks areformed discretely.

An arrangement for forming regions by impression is disclosed inJapanese patent application No. 4-71731, for example. The principles ofsuch an arrangement will briefly be described below. Such a magneticdisk can be fabricated by applying optical disk technology.Specifically, a glass master is prepared, and its surface is coated witha photoresist, for example. Then, a laser beam is applied to onlyportions of the photoresist where concavities will be formed. After thelaser beam has been applied, the photoresist is developed to remove theexposed portions. A stamper is formed from the glass master thus formed,and a large number of replicas are produced from the stamper. The stepsformed on the glass master have been transferred to each of thereplicas. A magnetic disk is completed by forming a magnetic film on thesurface to which the steps have been transferred.

In FIG. 2, those regions which are shown hatched are magnetized to Npoles corresponding to a logic "1", for example, of ID data, and thoseregions which are shown not hatched are magnetized to S polescorresponding to a logic "0".

The magnetic disk with concentric or spiral tracks formed thereon isrotated at a constant angular velocity (zone bit recording).

The tracks are formed between a position at one-half of the radius ofthe disk and an outermost circumference thereof, i.e., in a radiallyouter range covering one-half of the radius of the disk.

The disk has a diameter of 2.5 inches, 1.8 inches, or 1.3 inches. Thetrack pitch is 5.2 μm, the track width is 3.6 μm, and the guard band hasa width of 1.6 μm.

A magnetic disk having a diameter of 2.5 inches has a storage capacityof 200 MB on its both surfaces, and a magnetic disk having a diameter of1.8 inches has a storage capacity of 100 MB on its both surfaces.

FIG. 6 shows a magnetic disc according to the present invention and amechanism for actuating a magnetic head 21-13 for recording data orreproducing data from data regions.

On the magnetic disk 21-1, each segment is divided into a data recordingregion 21-3 (20-41 in FIG. 2) and a servo data recording region 21-2(20-40 in FIG. 2) as described with reference to FIG. 2. Servo datarecording regions 21-2 and data recording regions 21-3 are formed alonga path 21-21 of movement of the magnetic head 21-13.

In this device, the magnetic head 21-13 is mounted on the distal end ofan arm 21-11 (20-62 shown in FIG. 2) which is angularly movable about afulcrum (center of rotation) 21-12 (20-61 shown in FIG. 2). A voice coil21-15 is mounted on the arm 21-11 remotely from the end of the arm 21-11where the magnetic head 21-13 is mounted, across the fulcrum 21-12, anda magnet 21-14 is disposed below the voice coil 21-15. When apredetermined drive current is supplied to the voice coil 21-15 from adrive circuit 21-16, an electromagnetic force acts on the voice coil21-15 that is positioned in a magnetic flux generated by the magnet21-14, turning the arm 21-11 about the fulcrum 21-12. At this time, themagnetic head 21-13 moves along the path 21-21 which is of an arcuateshape extending about the fulcrum 21-12 and passing through the center21-4 of the magnetic disk 21-1.

In FIG. 6, the arm 21-11 is shown as a straight arm. However, the arm21-11 may be a bent arm.

FIG. 7 shows in detail a region dedicated for recording a servo signalin the servo data recording region 21-2.

In the embodiment shown in FIG. 7, a servo mark SM (the clock mark, thewobbled marks, the gray code, the unique pattern, and the home index) isformed as a substantially rectangular pattern defined by a curved linealong the path 21-21 of movement of the magnetic head 21-13 and curvedlines along tracks on the magnetic disk 21-1. Data regions of the IDrecording region 20-41H shown in FIG. 2 and all other regions formed byimpression are formed along the path of movement the magnetic head21-13.

In FIG. 7, since the servo mark SM is shown as exaggerated with respectto the tracks and the radius of the path 21-21, the sides of the servomark SM are represented by curved lines. Actually, however, the lengthof a side of the servo mark SM is extremely small as compared with thetracks and the radius of the path 21-21, and hence the servo mark SM isvirtually surrounded by almost straight lines.

Where the servo mark SM and other marks that are formed by impressionare arranged along the path 21-21, equal time intervals in a seek modeare not disrupted, and hence a PLL circuit (50-30 in FIG. 21) forgenerating a clock signal is prevented from being thrown out of phaselock in the seek mode. When data are recorded or reproduced by themagnetic head 21-13 with no bent angle (the bent angle is 0 and amagnetic gap line 21-41 parallel to the magnetic gap of the magnetichead 21-13 is perpendicular to the tracks), since the magnetic gap isperpendicular to the tracks, no azimuth loss is produced.

FIGS. 8A and 8B shows cross sections of the magnetic disk 21-1 of theabove arrangement. FIG. 8A shows a cross section perpendicular to thetracks, and FIG. 8B shows a cross section along the tracks. As shown inFIGS. 8A and 8B, a substrate 21-61 which is made of synthetic resin,glass, aluminum, or the like has steps formed on its surface, and amagnetic film 21-62 is formed on the stepped surface. Lower areas(concavities) of the steps serve as guard bands (GB), and higher areas(convexities) thereof as tracks (recording portions).

As shown in FIG. 8B, the data recording region 21-3 remains flat. In theservo data recording region 21-2, only those portions for recording aservo mark SM and a clock mark CM project (to same height as the datarecording region), and unrecorded regions where no servo signal isrecorded are lower than those portions (formed as concavities). Such adisk with concavities and convexities can be fabricated by the opticaldisk technology.

In the magnetic disk, the servo data recording regions and the IDrecording regions are formed along the path of movement of the magnetichead in the radially outward or inward direction. Therefore, equal timeintervals in a seek mode are maintained, and a PLL circuit forgenerating a clock signal is prevented from being thrown out of phaselock in the seek mode. It is also possible to suppress azimuth loss.

A process of magnetizing a disk with concavities and convexities will bedescribed below. There are 840 servo data recording regions 21-2positioned at equal intervals along the full circumference, and, asshown in FIG. 9, an impressed pattern of rectangular convexities 22-13each having a width of about 5 μm perpendicular to tracks and a lengthranging from about 0.7 to 2.9 μm parallel to the direction of travel ofthe disk is formed depending on the signal in the servo data recordingregions 21-2.

The convexities 22-13 and concavities 22-14 are magnetized in oppositedirections indicated by the arrows m1, m2 in FIG. 9 to write positioningsignals (such as wobbled marks, clock marks, and track numbers) on amagnetic disk 22-1.

In this example, the magnetic disk 22-1 (21-1 in FIG. 6) was rotated inthe direction indicated by the arrow a in FIG. 10A. While a first directcurrent was being supplied to a magnetic head 22-2 (the magnetic head ofa manufacturing apparatus), the magnetic head 22-2 was moved at trackpitches in the radial direction of the magnetic disk 22-1 to magnetize amagnetic layer 22-12 on the convexities 22-13 and the concavities 22-14on the magnetic disk 22-1 in one direction. The magnetic layer 22-12 wasdeposited on a nonmagnetic support 22-11.

Thereafter, as shown in FIG. 10B, while a second direct current which isopposite in polarity to the first direct current and has a value smallerthan the first direct current was being supplied to the magnetic head22-2, the magnetic head 22-2 was moved and scanned at track pitches inthe radial direction of the magnetic disk 22-1 to magnetize only themagnetic layer 22-12 on the convexities 22-13 on the magnetic disk 22-1in the opposite direction, thereby writing positioning signals.

The magnetic head 22-2 has a magnetic gap G having a gap length g0 of0.4 μm, a track width of 100 μm, and a coil winding of 56 turns with acentral tap (28+28). The magnetic head 22-2 floats over the magneticdisk 22-1 by a distance d of 0.13 μm at a relative speed of 6 m/s withrespect to the magnetic disk 22-1.

Since positioning signals can be written by a single magnetic head, anyhead replacing process is dispensed with, and the productivity of thedisk is increased.

FIG. 11 shows a detailed cross-sectional structure of a magnetic diskwhich is magnetized in this manner. A substrate 23-11 made of plastic,glass, or aluminum has a step (concavity) of 200 nm. If the substrate23-11 is made of glass, its thickness is 0.65 mm, and if the substrate23-11 is made of plastic, its thickness is 1.2 mm. Magnetic layers 23-12are formed on respective opposite surfaces of the substrate 23-11.

Each of the magnetic layers 23-12 includes a particle layer 23-12Aformed on the substrate 23-11 and having a particle density ranging from0.5 to 100 particles per 1 μm, preferably, a particle density of about10 particles per 1 μm. The particle layer 23-12A contains particles ofSiO₂ (spherical silica particles) 23-12a distributed therein at theabove particle density.

If the substrate 23-11 is made of glass or aluminum, the substrate 23-11can maintain rigidity relatively. If the substrate 23-11 is made ofplastic, it may not necessarily maintain sufficient rigidity, and itsdurability may be poorer than glass or aluminum. Because the substratehas large surface irregularities, it may be difficult to position amagnetic head closely to the magnetic layer 23-12 out of contacttherewith. The particle layers 23-12A of this magnetic disk allow suchsurface irregularities to be reduced in size since the surfaceirregularities are determined by the density and particle diameter ofthe particles 23-12a.

The particles (spherical silica particles) 23-12a can be attached to thesubstrate 23-11 by dipping. The particles have an average diameter of 50nm or less, preferably in the range of from 8 to 10 nm. When the averagediameter was 8 nm, the particle diameter distribution had a standarddeviation of 4.3 nm. The spherical silica particles were scattered inisopropyl alcohol so as to have a concentration of 0.01 wt %, and coatedon the surfaces of the substrate 23-11 at a pull-up speed of 125 mm/min.The coating ratio was 100%.

Since the particle density is determined by the dipping speed and theconcentration, it is possible to control the surface irregularities bycontrolling them. Attaching the particles by dipping makes it possibleto simplify the equipment. Dipping may be effected locally (e.g., in aninner or outer circumferential region).

The particles 23-12a may be inorganic fine particles of a material otherthan SiO₂.

On the particle layer 23-12A, there is formed a chromium layer 23-12Bhaving a thickness of about 80 nm. The chromium layer 23-12B functionsas an exchange binding film, has an effect of improving magneticcharacteristics, and particularly can increase coercive forces.

A cobalt platinum layer 23-12C is formed to a thickness of 40 nm on thechromium layer 23-12B. A protective film 23-12D of SiO₂ having athickness of 10 nm is spin-coated or coated on the cobalt platinum layer23-12C. A lubricant 23-12E is coated on the protective film 23-12D. Thelubricant 23-12E may be made of Z-DOl (trademark) of FOMBLIN Inc.

Then, the proportions of a data recording region and a servo datarecording region will be described below. As shown in FIG. 12, eachsegment is divided into a data recording region and a servo datarecording region. The data recording region is flat, and the servo datarecording region contains a servo pattern of clock marks, wobbled marks,and a gray code (more specifically, also sector numbers and tracknumbers in the ID recording region 20-41H shown in FIG. 2) that arerecorded as physical concavities and convexities.

As schematically shown in FIG. 13, a magnetic head held by a slider23-83 (a slider 40-57 shown in FIG. 19) that is supported on an arm23-81 (an arm 40-53 shown in FIG. 19) by a load beam 23-82 (a suspensionspring 40-56 shown in FIG. 19) is positioned a certain distance from amagnetic disk 23-84 by an air stream which is generated as the magneticdisk 23-84 rotates.

The smaller the distance between the magnetic head, and hence the slider23-83 and the magnetic disk 23-84, the greater a change in the magnetismdetected by the magnetic head, and the larger the reproduced output. Ifthe distance were too small, the magnetic head would be brought intocontact with the magnetic disk 23-84. Therefore, it is necessary to keepthe slider 23-83 spaced a certain distance from the magnetic disk 23-84.

Since the surface of the magnetic disk 23-84 (the magnetic disk 22-1shown in FIG. 10) is not flat, the distance between the slider 23-83 andthe magnetic disk 23-84 varies depending on the concavities andconvexities thereof. If a segment length S is sufficiently large withrespect to the length L of the slider and the servo data recordingregion is as long as the slider 23-83, then, as shown in FIG. 14, whenthe slider 23-84 starts to enter a servo data recording region(concavity) from a normal floating condition (floating condition over aflat region), the leading end of the slider begins to move downwardly,and hence pitch about its support. The trailing end of the slider istemporarily lifted, and thereafter the slider moves downwardly as awhole. At the bottom of the concavity, the slider runs while thepitching thereof which is caused when the slider starts to enter theconcavity is being dampened.

When the slider 23-83 moves out of the concavity, the leading endthereof is lifted, and the slider 23-83 pitches in a direction oppositeto the direction in which it has pitched upon entry into the concavity.The trailing end of the slider is temporarily depressed, and thereafterthe entire slider leaves the concavity. The slider returns to its normalfloating condition while its pitching movement is being dampened.

The above movement is carried out when the slider 23-83 moves over oneconcavity. Actually, the servo data recording region periodically occursat the segment period. To reduce clock jitter, it is preferable toreduce the segment period and increase the number of servo datarecording regions per track. However, if the number of servo datarecording regions per track is increased, then data recording regionsare reduced, resulting in a reduced recording capacity of the disk.Therefore, the number of servo data recording regions is determinedbased on a trade-off of the recording capacity of the disk and thejitter tolerance.

If it is assumed that, as shown in FIG. 15, the proportion of a servodata recording region to a segment is 23% and in the form of aconcavity, and the data recording region in the remaining 77% is in theform of a convexity, then the component of the segment period is addedto the characteristics with which the slider moves over one concavity asshown in FIG. 14. FIG. 16 shows the manner in which the distance betweenthe slider 23-83 and the magnetic disk 23-84 varies at the segmentperiod. In FIG. 16, the slider has a length of 1.8 mm, the magnetic disk23-84 rotates at a rotational speed of 2700 rpm, and the number ofsegments per one revolution is 420. It can be seen from FIG. 16 that thedistance between the slider 23-83 and the magnetic disk 23-84 greatlyvaries at the segment period.

FIG. 64 shows simulated values of changes in the amount of floating ofthe slider 23-83 at the time it moves over the servo data recordingregion, with the ratio of the servo data recording region to the datarecording region per segment being as a parameter. The conditions in thesimulation are that the number of segments per track is 420, the amountof floating is 0.11 μm, the peripheral speed is 12.8 m/s, the rotationalspeed of the disk is 45 Hz, and the skew angle is 0 degree. The depth ofthe concavity of the serve data recording region is 0.1 μm.

As shown in FIG. 64, as the ratio of the servo data recording region tothe data recording region increases from 10:90 to 23:77 to 30:70, thechange in the amount of floating increases successively from 13.0 nm to28.0 nm to 32.0 nm. Therefore, it can be understood that the smaller theproportion of the servo data recording region, the smaller the change inthe amount of floating of the slider 23-83 over the magnetic disk. Ifthe proportion of the servo data recording region increases, therecording capacity decreases, and the change in the amount of floatingof the slider increases. In worst cases, the change in the amount offloating of the slider is not dampened sufficiently on a flat surface,making it difficult to record and reproduce data stably. It ispreferable that the proportion of the servo data recording region (aregion where a concavity is formed) per track be 40% or less.

The aspects of the recording head 10-3 and the playback head 10-4 shownin FIG. 1 will be described below.

In FIG. 177, on a floating-type slider (the slider 23-83 shown in FIG.13) or a base 30-6 attached thereto, there are deposited first andsecond magnetic layers 30-3, 30-4 facing an ABS (Air Bearing Surface)30-7 that contacts or confronts the magnetic disk, the first and secondmagnetic layers 30-3, 30-4 serving as a shield for the playback head. AnMR element 30-1 comprising an MR (magnetoresistance) thin film and abias conductor 30-18 are disposed such that they are sandwiched betweenthe first and second magnetic layers 30-3, 30-4 with a nonmagneticinsulating layer 30-8 therebetween, thereby making up an MR playbackhead. The bias conductor 30-18 is arranged across the MR element 30-1 tomake the MR element 30-1 magnetized in a given direction to cause themagnetoresistance characteristics thereof to work in a characteristicregion which exhibits excellent linearity and high sensitivity.

A third magnetic layer 30-5 is deposited outwardly of the secondmagnetic layer 30-4, i.e., on its side remote from the MR element 30-1,with the nonmagnetic insulating layer 30-8 therebetween. Aspiral-pattern head winding (30-2 in FIG. 18) is formed between thesecond and third magnetic layers 30-4, 30-5 so as to surroundmagnetically coupling portions between their rear portions spaced fromthe ABS 30-7.

There are thus constructed a shield-type MR magnetic head (playbackhead) with the MR element 30-1 disposed between the first and secondmagnetic layers 30-3, 30-4, and an Ind (induction)-type magnetic head(recording head) with the head winding wound on a magnetic path which iscomposed of the second and third magnetic layers 30-4, 30-5.

The track width of the MR playback head is limited by a width W_(TH) Ofthe MR element 30-1 which faces the ABS 30-7, and the track width of theInd-type recording head is limited by a width W_(TI) of the thirdmagnetic layer 30-5 which face the ABS 30-7. The width W_(TH) of the MRelement 30-1 is of a relatively large value of 5.2 μm (a width equal tothe track pitch), for example, and the width W_(TI) of the thirdmagnetic layer 30-5 is of a relatively small value 4.0 μm (a widthsmaller than the track pitch), for example.

Using such an MR/Ind-composite thin-film head, data is recorded on andreproduced from a discrete-type magnetic disk having a track pitch of5.2 μm, a track width of 3.6 μm, and a guard band of 1.6 μm, i.e., atrack density of 4885 TIP (Track Per Inch). It is possible to avoidchanges in the reproduced output without inviting an increase in theplayback noise, and to increase the reproducing characteristics.

A cross-sectional structure of a magnetic head will be described belowwith reference to FIG. 18. The first and second magnetic layers 30-3,30-4 are disposed on the base 30-6 in facing relationship to the ABS30-7, the first and second magnetic layers 30-3, 30-4 sandwiching andshielding the MR element 30-1. The nonmagnetic insulating layer 30-8serving as a magnetic gap upon recording data and the third magneticlayer 30-5 are disposed on the first and second magnetic layers 30-3,30-4 in facing relationship to the ABS 30-7. The reference numeral 30-2represents the spiral-pattern head winding formed between the second andthird magnetic layers 30-4, 30-5 so as to surround magnetically couplingportions between their rear portions. The second and third magneticlayers 30-4, 30-5 constitute a recording head.

The MR element 30-1 has a leading-end electrode 3015 on its side heldagainst the ABS 30-7, and a trailing-end electrode 30-16 on the otherend thereof for detecting a signal magnetic field from a magnetic diskthat is positioned in contact with or in confronting relationship to theABS 30-7. The reference numeral 30-18 indicates a bias conductor forgiving a bias magnetic field to the MR element 30-1. The second magneticlayer 30-4 functions as a shield for the MR element 30-1 uponreproducing data, and as an inductive core upon recording data.

The distance (recording gap) between the upper surface of the secondmagnetic layer 30-4 and the lower surface of the third magnetic layer30-5 is 0.6 μm, and the distance between the center of the MR element30-1 and the upper surface of the first magnetic layer 30-3 is 2 μm.

The composite thin-film head can increase the reproduced output becausethe track width of the playback head is large.

When data are recorded on and reproduced from the discrete-type magneticdisk using the composite thin-film head, it is possible to reduceplayback fringing and provide a large margin with respect to apositional shift between the playback head and a track on the magneticdisk. Therefore, any changes in the reproduced output can be suppressed,and the reproduced output characteristics can be increased.

Each of the widths W_(TI), W_(TW) may be an integral multiple of thetrack width. The recording head and the playback head may double eachother.

FIG. 19 shows a structure of an arm on which the magnetic head(recording head and playback head) described with reference to FIGS. 5,6, 17, and 18 is mounted. As shown in FIG. 19, magnetic disks 40-52 arerotatably mounted on a lower casing 40-51 by a spindle motor (10-21shown in FIG. 59). An arm 40-53 is angularly movably mounted on thelower casing 40-51 for angular movement about a shaft 40-54. As shown ina cross-sectional view of FIG. 20, ball bearings 40-55 are disposedbetween the shaft 40-54 and the arm 40-53 for reducing friction at thetime the arm 40-53 is angularly moved.

A suspension spring 40-56 is attached to the distal end of the arm40-53, and a slider 40-57 is attached to the distal end of thesuspension spring 40-56 by a gimbal spring (not shown). The magnetichead (recording head and playback head) is mounted on the slider 40-57.There are two magnetic disks 40-52, each having magnetic films disposedon opposite surfaces thereof. A total of four sliders are disposed inconfronting relationship to the opposite surfaces of the magnetic disks.

A voice coil 40-63 (21-15 shown in FIG. 6) is attached to the other endof the arm 40-53. Magnets 40-61, 4062 (21-14 shown in FIG. 6) aredisposed above and below, respectively, of the voice coil 40-63.Magnetic fluxes are directed locally from the magnet 40-61 toward themagnet 40-62 and also from the magnet 40-62 toward the magnet 40-61. Thecoil 40-63 is disposed across the magnetic fluxes. As a result, when adrive current flows through the coil 40-63, electromagnetic forces aregenerated to cause the coil 40-63 and hence the arm 40-63 to turn aboutthe shaft 40-54. Consequently, the slider 40-57 (and hence the magnetichead mounted thereon) is moved to a certain radial position over themagnetic disk 40-52.

The aspect of the clock signal generator 10-6 shown in FIG. 1 will bedescribed below.

FIG. 21 shows an arrangement of an embodiment in which the presentinvention is applied to a magnetic hard disk device. Double-sidedmagnetic disks 50-1A, 50-1B (40-52 shown in FIG. 9) are rotated by aspindle motor 50-2. Magnetic heads 50-3A, 50-3B are supportedrespectively by arms 50-4A, 50-4B, and can be angularly moved about acenter 50-5C of rotation by a voice coil motor (VCM) 50-5 to followtracks 50-502 on upper surfaces of the magnetic disks 50-1A, 50-1B forwriting data on and reading data from these tracks.

The two magnetic disks 50-1A, 50-1B constitute a cylinder 50-100.Although not shown, there are two magnetic heads for writing data on andreading data from lower surfaces of the double-sided magnetic disks50-1A, 50-1B. These magnetic heads are also supported by the arms 50-4A,50-4B for angular movement about the center 50-5C by the VCM 50-5. Asdescribed above with reference to FIG. 2, a plurality of clock marks20-11 for giving a time standard are impressed in data tracks on thesurfaces of the magnetic disks 50-1A, 50-1B. The reference numeral 50-6represents the center of rotation of the spindle motor 50-2, i.e., thecenter of rotation of the magnetic disks 50-1A, 50-1B.

A host computer 50-50 supplies commands including a write command, aread command, etc. to a controller 50-70 through an interface cable50-60. The controller 50-70 outputs control signals for controlling themagnetic hard disk device to a signal processor 50-20.

Reproduced signals read from the disks 50-1A, 50-1B by the magneticheads 50-3A, 50-3B are amplified to a certain amplitude by a playbackamplifier 50-21. The playback amplifier 50-21 supplies its output signalto a clock extractor 50-22, a track position error detector 50-23, ahome index extractor 50-24, and a track address decoder 50-80.

An extracted clock signal (the clock mark 20-11) produced by the clockextractor 50-22 is supplied to a track eccentricity measuring unit50-25. A home index signal 20-73 (FIG. 4), i.e., a rotational phaseorigin signal, produced by the home index extractor 50-24 is alsosupplied to the track eccentricity measuring unit 50-25. The trackposition error detector 50-23 generates a track position error signal(tracking error signal) from the difference between reproduced levels ofa pair of wobbled marks 20-12, 20-13, and supplies the tracking errorsignal to a tracking servo circuit 50-40 and an off-track determiningcircuit 50-90.

The track eccentricity measuring unit 50-25 measures an amount ofeccentricity of the data track circle 50-502 with respect to the centralaxis 50-6 as a function of an angular position θ on the disk where thehome index on the disk is generated at a position represented by anangular coordinate value of 0, and stores the measured amount ofeccentricity in a table in an eccentricity memory 50-26. The amount ofeccentricity is supplied to a PLL circuit 50-30 for correcting a timebase error of the clock signal, and also to a tracking servo circuit50-40 for controlling the VCM 50-5.

One of the features of the embodiment shown in FIG. 21 is that theamount of eccentricity stored in the memory 50-26 is read by a reader50-27 in synchronism with the rotation of the disk and converted by aD/A converter 50-28 into an analog signal, which is then compensated forby a feed-forward compensator 50-29, i.e., converted into a speed signalthat is fed forward as a control voltage for a voltage-controlledoscillator (VCO) 50-35 of the PLL circuit 50-30.

The PLL circuit 50-30 includes a phase comparator 50-31, a loop filter50-32 for effecting filtering such as low-path filtering on an outputsignal from the phase comparator 50-31, and the voltage-controlledoscillator 50-35 for outputting a clock signal whose phase and frequencydepend on an output signal from the loop filter 50-32. The phasecomparator 50-31 outputs the phase difference between the clock signalextracted by the clock extractor 22 and a clock signal outputted by thevoltage-controlled oscillator 50-35 and fed back through a divide-by-Nfrequency divider 50-36.

The embodiment shown in FIG. 21 resides in that an analog adder(operational amplifier) 50-33 is disposed between the loop filter 50-32and the VCO 50-35 for adding a signal supplied from the feed-forwardcompensator 50-29 through a switch 50-34 to the signal outputted fromthe loop filter 50-32, and supplying the sum signal to the VCO 50-35.Each of the loop filter 50-32 and the adder 50-33 may comprise a digitalcalculating element.

With this arrangement, the VCO 50-35 is driven by not only the outputsignal from the phase comparator 50-31 but also a track circleeccentricity representing voltage supplied through the reader 50-27, theD/A converter 50-28, the feed-forward compensator 50-29, and the switch50-34. Therefore, the VCO 50-35 follows a pulse signal in synchronismwith 840 clock marks per revolution, for example, which are generatedfrom the disk, in a closed loop mode, and also operates in an open loopmode with a signal predicting a present instantaneous amount ofeccentricity and supplied from the memory 50-26.

While a disk with eccentricity is operating, the clock from the disk asobserved from the playback head fixed in the direction of θ (thedirection of rotation of the disk) suffers fluctuations (jitter) in thedirection of the time axis. Most of the component of the fluctuationswhich corresponds to the rotational frequency (60 Hz) intentionallyoscillates the VCO 50-35 in the open loop mode to cause the clock signaloutputted from the clock extractor 50-22 and the clock signal outputtedfrom the VCO 50-35 to be closely in phase with each other at about ±20ns (nanoseconds).

Because the clock signals are held closely in phase with each other inthe open loop mode, the closed loop mode may only be necessary to cancelout mainly a high-frequency component (whose frequency is several toseveral tens times the rotational frequency) of the fluctuationcomponent which has small amplitudes. Finally, therefore, the outputsignal from the VCO 50-35 can be kept very closely in phase with theclock signal outputted from the clock extractor 50-22 at ±1 ns or less.

As described above with reference to FIG. 2, data track circles areproduced by a cutting machine having a feed accuracy of about 0.01microns as with the optical disk fabrication apparatus. Therefore, thecircularity of the data track circles has an error having a value whichis sufficiently smaller than 1 microns. When such a disk is mounted onthe rotatable shaft (the shaft 40-54 shown in FIG. 19), the center ofthe disk, i.e., the center of the data track circles, suffers anattachment error ranging from 10 to 50 μm with respect to the rotationalshaft.

A process of measuring such a deviation (eccentricity) will be describedin detail later on with reference to FIGS. 25 through 23. First, such aprocess will briefly be described with reference to FIG. 22.

In FIG. 22, the reference numeral 50-500 indicates the center of thetrack 50-502, and the reference numeral 50-501 indicates the center ofrotation of the disk. The playback head 50-3 is supported on the arm50-4 and positioned by the tracking servo circuit 50-40 so as to tracethe central axis of the track 50-502.

If it is assumed that the track 50-502 has a radius r0 (m), aneccentricity δ (m), and a rotational speed N (Hz), then the track 50-502has an average peripheral speed V0 as follows:

    V0=2πr0×N (m/sec).

If the number of pulses produced by clock marks (indicated by round dotsin FIG. 22) contained in the circular track 50-502 having the radius r0is M (pulses/revolution), then an interpulse distance L0 is given by:

    L0=2πr0/M.

The time T0 required for the playback head 50-3 to path through theinterpulse distance L0 is:

    T0=L0/V0=(2πr0/M)/(2πr0×N)=1/(N×M).

For example, if N=60.0 Hz and M=840, then the time T0 is:

    T0=19.841 (μsec).

The pulse period T2 in a region where the radius is increased to r2=r0+δby the eccentricity, and the pulse period T1 in a region where theradius is reduced to r1=r0-δ by the eccentricity are given as follows:

    T2=2πr0/M(2πr2×N)=r0/r2×(N×M),

    T1=2πr0/M(2πr1×N)=r0/r1×(N×M).

Therefore, when r0=20 mm and r2=20.05 mm, the time period T2 becomesT0×1.0025, and hence varies by 0.25%. While this change is very small,it can be measured relatively accurately as it is a quantity in timedomain.

In this example, since T0=19.841 (μs), T2=19.891 (μs), and T1=19.792(μs), the average value of T and each of maximum and minimum valuesthereof differ from each other by about 50 ns (nanoseconds). Since suchdifferences can be measured with sufficient accuracy according to thepresent electronic circuit technology, the measurement of eccentricitiesresults in the measurement of time intervals.

Advances and delays of the signal as it is observed against theeccentricity in one revolution of the disk are stored as digitalnumerical values in the memory 50-26, thereby completing the generationof an eccentricity table.

A feed-forward control process of the VCO 50-35 using the eccentricitytable stored in the memory 50-26 is carried out as follows: First, thecontents of the memory 50-26 are read in synchronism with the rotationalphase of the disk by the reader 50-27, and converted into an analogvoltage by the D/A converter 50-28. The analog signal is compensated forphase by the feed-forward compensator 50-29, which is composed of a coilL, a capacitor C, and a resistor R (not shown), and then applied throughthe switch 50-34 and the analog adder 50=33 to the VCO 50-35. Theoscillating phase of the VCO 50-35 varies largely as indicated by thesolid-line curve in FIG. 23 when no feed-forward compensation signal isapplied thereto. When a feed-forward compensation signal is applied tothe VCO 50-35, the oscillating phase of the VCO 50-35 becomes close to0° as indicated by the broken-line curve in FIG. 23.

FIG. 24 shows a second embodiment of the clock signal correcting circuitaccording to the present invention.

In the embodiment shown in FIG. 21, displacements (eccentricities) of atrack itself with respect to various rotational positions of the diskare stored in the memory 50-26. In the embodiment shown in FIG. 24,however, displacements of a track itself are temporarily stored in atemporary memory 50-251, and then calculations equivalent to those inthe feed-forward compensator 50-29 shown in FIG. 21 are effected on thestored contents of the temporary memory 50-251 by a calculating unit50-252, after which they are stored in a memory 50-26A. Therefore, thequantities stored in the memory 50-26A are speeds corresponding toeccentricities.

In the arrangement shown in FIG. 24, the feed-forward compensator 50-29shown in FIG. 21 may be dispensed with. Specifically, the compensator50-29 or filter shown in FIG. 21 is required to be composed ofhigh-speed devices as it operates on a real-time basis. Sinceeccentricities may need to be measured once in a day, if calculationsequivalent to those in the feed-forward compensator 50-29 shown in FIG.21 are effected as with the embodiment shown in FIG. 24, then thecalculating unit 50-252 may be composed of an inexpensivegeneral-purpose processor. The arrangement shown in FIG. 24 is alsoadvantageous in that operations which are difficult to carry out in ananalog arrangement can be performed.

In the embodiment shown in FIG. 24, a stored content selector 50-27Aselectively picks up quantities (i.e., speeds), corresponding to amountsof eccentricity of a plurality of disk surfaces, which are stored in thememory 50-26A based on a command from the controller 50-70.

Since the embodiment shown in FIG. 24 is arranged as described above, ameasured eccentricity produced in the same manner as with the embodimentshown in FIG. 21 is adjusted to certain amplitude-phase characteristicsby the calculating unit 50-252, and then stored in the memory 50-26A.Such an eccentricity measuring operation is repeated independently foreach of the surfaces of plural disks at suitable times after the powersupply switch is turned on. Since there are four disk surfaces, theeccentricity measuring operation is carried out four times using theheads that correspond respectively to the disk surfaces. Therefore, thememory 50-26A stores four types of eccentricities.

Operation at the time the controller 50-270 selects the disk 50-1B (seeFIG. 21) will be described below. At this time, the selector 50-27Aoutputs eccentricity data detected by the head 50-3B from theinformation stored in the memory 50-26A, in synchronism with therotation of the disk 50-1B. The outputted eccentricity data represent aphase-compensated amount of eccentricity at angular position coordinateson the disk which correspond to memory addresses.

The outputted eccentricity data are converted by the D/A converter 50-28into an analog voltage, which is applied to the VCO (voltage-controlledoscillator) 50-35 through the adder 50-33. The VCO 50-35 accuratelycancels out advances and delays of the clock signal which are caused bythe eccentricity of the disk, and outputs pulses in very close phasewith the clock signal reproduced from the disk.

In the embodiment shown in FIG. 24, the calculated amounts ofeccentricity from the calculating unit 50-252 are stored in the memory50-26A, and the calculated amount of eccentricity which corresponds tothe disk surface to be processed is read out. However, the amounts ofeccentricity themselves may be stored, and the calculated amount ofeccentricity which corresponds to the disk surface to be processed maybe read out.

According to the above embodiment of the present invention, it ispossible to generate a clock signal which is highly accuratelysynchronous with clock marks impressed on a disk. If such a clock signalis used in the detection of a track position error signal or thedemodulation of a data code, highly good results can be obtained. Thegain of an eccentricity frequency range may be increased withoutincreasing the band of a clock regenerating loop.

A process of measuring an amount of eccentricity will be describedbelow.

FIG. 25 shows the relationship between a magnetic disk on which N clockmark signals (20-11 shown in FIG. 2) are physically stored at equalintervals along the full circumference of a circular data track and thepath of a playback head, i.e., a signal reading head, that is fixed at aposition spaced a certain radius from the center of the disk that ischucked. In FIG. 25, the reference numeral 51-500 represents the centerof the circular data track. Data tracks 50-D3 through 50-D7 are formedconcentrically around the center 51-500, and the N clock mark signals51-CM (20-11 shown in FIG. 2) are physically recorded at equal intervalsalong the full circumference of each circular data track.

When the magnetic disk with the above circular data tracks is chucked ona spindle motor shaft 51-501, the magnetic disk suffers an eccentricity51-511. The reference numeral 51-503 represents a circular path of aplayback head, i.e., a signal reading head, that is fixed at a positionspaced a certain radius 51-510 from the center 51-501 of the disk thatis chucked. When the circular path 51-503 is closest to the center51-500, the time in which the head travels through a distance 51-513between clock mark signals 51-CM on the circular path 51-503 becomesshortest. When the circular path 51-503 is furthest from the center51-500, the time in which the head travels through a distance 51-514between clock mark signals 51-CM on the circular path 51-503 becomeslongest. This is because the radius 51-510 of rotation of the disk isthe same, and the head travels at the same speed.

Time intervals of clock mark reproduced signals reproduced from theplayback head, i.e., the signal reading head, that is fixed at aposition spaced the certain radius 51-510 from the center 51-501 of thedisk that is chucked, are measured and utilized to produce amounts ofeccentricities corresponding to angular positions on the disk which arecaused by the eccentricity 51-511.

FIG. 26 shows in specific details a time interval measuring unit 51-70and an eccentricity calculating unit 51-25 of the eccentricity measuringunit 50-25 shown in FIG. 21. An eccentricity recording unit 51-26corresponds to the eccentricity recording unit 50-26 shown in FIG. 21.In the example shown in FIG. 26, the time interval measuring unit 5170comprises a flip-flop 51-71, a counter 51-72, an inverter 51-73, acounter 51-74, an oscillator 51-75, and a switch 51-76. The eccentricitycalculating unit 51-25 comprises a CPU 51-251, a memory 51-252, latches51-253, 51-254, and a calculating unit 51-255. The eccentricityrecording unit 51-26 comprises a memory 51-260. The CPU 51-251 has amemory access function for the memory 51-252.

The flip-flop 51-71 outputs a pulse signal 51-TD which switches betweenhigh and low TTL levels each time a clock mark reproduced signal 51-CMSreproduced from the disk arrives. The pulse signal 51-TD is supplieddirectly to the counter 51-72, and also inverted by the inverter 51-73and supplied to the counter 51-74.

The counter 51-72 measures, with the oscillator 5175, a time interval inwhich the pulse signal 51-TD is high, and outputs a measured timeinterval value 51-CTA. The counter 51-74 measures, with the oscillator51-75, a time interval in which the pulse signal outputted from theinverter 51-73 is high, i.e., a time interval in which the pulse signal51-TD is low, and outputs a measured time interval value 51-CTB.

The switch 51-76 outputs the measured time interval value 51-CTAoutputted from the counter 51-72 and the measured time interval value51-CTB outputted from the counter 51-74, alternatively as a count 51-250according to a control signal 51-CNT which is outputted from the CPU51-251 based on a home index signal 51-HIS (20-73 shown in FIG. 4). Thememory 51-252 successively stores (N+N/2) measured time interval values51-250 (for half revolution) supplied from the switch 51-76 according toa control signal 51-CS2 and an address 51-AS2 that are outputted fromthe CPU 51-251 based on the home index signal 51-HIS.

The measured time interval values stored in the memory 51-252 are readout according to the control signal 51-CS2 and the address signal 51-AS2which are outputted from the CPU 51-251. The pth measured time intervalvalue that has been read out is held by the latch 51-253 according to alatch signal 51-LHA outputted from the CPU 51-251. The (p+N/2)thmeasured time interval value (at a sampling position spaced from the pthsampling position by half revolution of the disk) that has been read outis held by the latch 51-254 according to a latch signal 51-LHB outputtedfrom the CPU 51-251.

The subtractor 51-255 subtracts the (p+N/2)th measured time intervalvalue from the pth measured time interval value. The subtractor 51-255effects such a subtraction for each of p=1 through N. The N results ofsubtraction produced from the subtractor 51-255 are successively storedin the memory 51-260 according to a control signal 51-CS1 and an addresssignal 51-AS1 that are outputted from the CPU 51-251 based on the homeindex signal 51-HIS.

The results of subtraction stored in the memory 51-260 represent amountsof eccentricity corresponding to angular positions on the disk, andindicate distances produced between the circular data tracks 51-D3 andthe head path 51-503 (see FIG. 25) due to the eccentricity. The resultsof subtraction are read out of the memory 51-260 as amounts 51261 ofeccentricity according to the control signal 51-CS1 and the addresssignal 51-AS1 that are outputted from the CPU 51-251 based on the homeindex signal 51-HIS, and can be used as an eccentricity distance tablefor correcting eccentricities.

FIG. 27 shows the relationship between clock mark reproduced signals51-CMS and time intervals that are measured in the arrangement shown inFIG. 26. In FIG. 27, it is assumed that the count of a time intervalbetween an nth clock mark reproduced signal 51-CMS and an (n+1)th clockmark reproduced signal 51-CMS is represented by t(n). If the count atthe time the circular path 51-503 shown in FIG. 25 is remotest from thecenter 51-500 of the circular data tracks is represented by t(k), thenthe count at the time the circular path 51-503 is closest to the center51-500 of the circular data tracks is t(k+N/2).

FIG. 28 shows time intervals of the clock mark reproduced signalsmeasured by the time interval measuring unit 51-70 shown in FIG. 26,i.e., time intervals of the clock mark reproduced signals measured bythe memory 51-70, i.e., a series of counts 51-250 stored in the memory51-252, as related to data numbers (sampling numbers). In FIG. 28, thecount at the time the circular path 51-503 shown in FIG. 25 is remotestfrom the center 51-500 of the circular data tracks is t(k), and thecount at the time the circular path 51-503 is closest to the center51-500 of the circular data tracks is t(k+N/2).

FIG. 29 shows amounts of eccentricity stored in the memory 51-260 of theeccentricity memory 51-26 arranged as shown in FIG. 26 and related tothe rotational angle of the disk, i.e., distances produced between thecircular data tracks and the head path 51-503 (see FIG. 25) due to theeccentricity. The illustrated amounts of eccentricity are measuredresults produced by subtracting the (p+N/2)th measured time intervalvalue from the pth measured time interval value. The series of data51-261 stored in the memory 51-260 can be used as an eccentricitydistance table corresponding to disk angular positions for correctingeccentricities.

FIG. 30 shows an arrangement of another embodiment of the eccentricitymeasuring unit 25 shown in FIG. 21. A time interval measuring unit51-70C measures, using the home index signal 51-HIS, a time intervalbetween an (n+m)th clock mark reproduced signal 51-CMS (n is an integerfrom 1 to N) and an (n+m+1)th clock mark reproduced signal 51-CMS whichare reproduced from the disk, with respect to each integer m=0 through(N+N/2-1). The measured time interval values measured by the timeinterval measuring unit 51-70C are successively stored in a memory51-252C according to a control signal 51-CS8 and an address signal51-AS8 which are outputted from a memory access unit 51-251C based onthe home index signal 51-HIS.

The measured time interval values stored in the memory 51-252C are readtherefrom according to the control signal 51-CS8 and the address signalA51-S8 which are outputted from the memory access unit 51-251C based onthe home index signal 51-HIS. An adder 51-255C adds N/2 measured timeinterval values ranging from the pth measured time interval value to the(p+N/2) measured time interval value (for half revolution) with respectto each integer p=1 through N. The results of addition produced by theadder 51-255C are successively stored in a memory 51-256C according to acontrol signal 51-CS9 and an address signal 51-AS9 which are outputtedfrom the memory access unit 51-251C based on the home index signal51-HIS.

N results of addition produced by the adder 51-255C (for one revolution)are added by an adder 51-257C, and the result of addition produced bythe adder 51-257C is divided into 1/N by a divider 51-258C which outputsan average value 51-AV3.

The results of addition stored in the memory 51-256C are successivelyread therefrom according to the control signal 51-CS9 and the addresssignal 51-AS9 which are outputted from the memory access unit 51-251Cbased on the home index signal 51-HIS. A subtractor 51-259C divides thekth result of subtraction that has been read by the average value AV3for each integer k=1 through N. The results of subtraction produced bythe subtractor 51-259C are successively stored in a memory 51-260Caccording to a control signal 51-CS10 and an address signal 51-AS10which are outputted from the memory access unit 51-251C based on thehome index signal 51-HIS.

The results of subtraction stored in the memory 51-260C representamounts of eccentricity corresponding to angular positions on the disk,and indicate distances produced between the circular data track 51-D3and the head path 51-503 (see FIG. 25). The results of subtraction areread out of the memory 51-260C as amounts 51-261C of eccentricityaccording to the control signal 51-CS10 and the address signal 51-AS10which are outputted from the memory access unit 51-251C based on thehome index signal 51-HIS, and can be used as an eccentricity distancetable for correcting eccentricities. Therefore, the embodiment shown inFIG. 30 is effective to reduce noise and reduce the lengths of thecounters used in measuring time intervals.

FIG. 31 shows the relationship between clock mark reproduced signals andtime intervals 51-250C that are measured in the embodiment shown in FIG.30. In FIG. 31, a time interval between a second clock mark reproducedsignal 51-CMS and an (n+1)th clock mark reproduced signal 51-CMS isrepresented by t(n).

FIG. 32 shows time intervals 51-250C of the clock mark reproducedsignals measured by the time interval measuring unit 51-70C, and anaverage value 51-AV3 outputted from the divider 51-258C in theembodiment shown in FIG. 30. The time interval measuring unit 51-70Cmeasures a minimum time unit which the measuring means has. When theminimum time unit is coarse with respect to the amounts of eccentricity,the series 51-250C of time interval data is stepped with respect to thedisk angular positions. If the number N/2 of time interval data 51-250Cwhich have been measured stepwise and are added by the adder 51-255C issufficiently large, the obtained eccentricity information can smoothlybe reproduced with respect to the disk angular positions.

FIG. 33 shows amounts 51-261C of eccentricity stored in the memory51-260C in the embodiment shown in FIG. 30 and related to the rotationalangle of the disk, i.e., distances produced between the circular datatracks 51-D3 and the head path 51-503 (see FIG. 25) due to theeccentricity. The series of data 51-261C stored in the memory 51-260Ccan be used as an eccentricity distance table corresponding to diskangular positions for correcting eccentricities.

In the foregoing embodiments, eccentricity is measured from clock marks.However, it may be measured from the servo pattern (the unique pattern20-72, the gray code 20-71, the wobbled marks 20-12, 20-13, etc.)recorded in the servo data recording region 20-40 shown in FIG. 2.

The aspect of the tracking servo unit 10-7 shown in FIG. 1 will bedescribed below.

FIG. 34 shows an arrangement of an embodiment for effecting trackingcontrol in a magnetic disk device. A magnetic disk 60-2 (50-1A, 50-1Bshown in FIG. 21) is rotated by a spindle motor 60-8. A magnetic head60-10 (having the structure shown in FIGS. 17 and 18) is supported by anarm 60-12, and can be angularly moved by a voice coil motor (VCM) 60-14for writing data on and reading data from the magnetic disk 60-2.

As has been described above with reference to FIG. 2, the magnetic disk60-2 has a number of concentric or spiral tracks 60-4 in which there arerecorded servo patterns including a rough pattern (gray code 20-71) andan accurate pattern (wobbled marks 20-12, 20-13) for positioning(tracking control) the magnetic head 60-10. The spindle motor 60-8 has arotatable shaft that is driven at 3600 rpm, for example.

A playback amplifier 60-21 amplifies an output signal from the magnetichead 60-10 and outputs the signal to a track position error detector60-23 and a track address decoder 60-32. The track address decoder 60-32reads a track address of gray code from the inputted signal, comparesthe track address with the address of a desired track (to be accessed),and outputs the difference as a rough signal to a position generator60-36. The track position error detector 60-23 detects a signalcorresponding to wobbled marks from the inputted signal, and outputs atracking error signal corresponding to a deviation of the magnetic head60-10 from the track. The tracking error signal is converted by an A/Dconverter 60-34 into an analog signal, which is supplied to the positiongenerator 60-36.

The position generator 60-36 adds the output signal from the trackaddress decoder 60-32 and the tracking error signal from the A/Dconverter 60-34, thereby generating a positional signal (final trackingerror signal).

A feedback controller 60-40 comprises a subtractor 60-41 for determiningthe difference between the positional signal from the position generator60-36 and a signal indicative of a servo reference of a track (thissignal corresponds to a position where to place the magnetic head, andbecomes 0 when the position of the magnetic head is at the center of atrack), and outputting a position error signal, components 60-42, 60-43,60-44 for effecting a PID (Proportional plus Integral plus Derivative)action on the position error signal, and an adder 60-45 for addingoutput signals from these components 60-42, 60-43, 60-44. The feedbackcontroller 6040 energizes the VCM 60-14 through a D/A converter 60-70and a drive amplifier 60-80 to position the magnetic head 60-10 on areference position (normally at the center) of a track 60-4. Theforegoing arrangement is of known art.

The embodiment shown in FIG. 34 includes in a feed-forward controller60-60 having an eccentricity memory 60-26 and an adder 60-56 for addinga signal which is produced by phase-compensating (equalizing) an outputsignal from the feed-forward controller 60-60 with a phase compensator60-75 to an output signal from the feedback controller 60-40 andsupplying a sum signal to the D/A converter 60-70. The eccentricitymemory 60-26 of the feed-forward controller 60-60 may comprise theeccentricity memory 50-26 shown in FIG. 21 (the eccentricity memory51-26 shown in FIG. 26). Thus, the eccentricity memory 60-26 stores datacorresponding to eccentricities as described above with reference toFIGS. 25 through 33.

Feed-forward data stored in the eccentricity memory 60-26 are referredto at the same timing as the above eccentricity measuring operation forone revolution, and outputted as a feed-forward control output signal60-57. This signal is phase-compensated (advanced in phase) by the phasecompensator 60-75, and then applied to the adder 60-56. The adder 60-56adds the signal to the output signal 60-52 from the feedback controller60-40, and supplies the sum signal through the D/A converter 60-70 tothe VCM drive amplifier 60-80. The drive amplifier 60-80 energizes theVCM 60-14 based on the supplied signal.

A reference signal for referring to the control quantity data stored inthe eccentricity memory 60-26 at the same timing as when eccentricitiesare measured may be a signal which is reproduced by the head 60-10 asrepresenting a servo pattern 60-6 (e.g., clock marks) recorded on thedisk 60-2, or a rotational angle signal from the spindle motor 608.

With the above arrangement, it is possible to reduce a normalpositioning error with respect to a track reference position to beachieved by a closed control loop which is composed of the positiongenerator 60-36, the feedback controller 60-40, the D/A converter 60-70,and the VCM drive amplifier 60-80. The principles of such an operationare as follows:

FIG. 35 is a block diagram of a simplified arrangement of the embodimentshown in FIG. 34. Denoted in FIG. 35 at 60-151 is a transfer function ofa circuit system for energizing the VCM 60-14 (i.e., a feedback controlblock 60-40), a transfer function 60-152 of the VCM 60-14 to becontrolled, a reference valued of a target track, a head position x, atrack eccentricity, and an observed position y. These components are thesame as the known art. Denoted at Uff is a feed-forward control outputsignal which is newly added according to the present invention.

A residual disturbance component d' in FIG. 35 is represented by thefollowing equation:

    d'=d+G(jω)·Uff.

When a tracking control process is effected using the feed-forward datacalculated by the above process, the feed-forward control output signalUff is expressed by:

    Uff=-inverse(G(jω))·d

where (G(jω))·inverse (G(jω))=1, and thus d'=0.

In the embodiment shown in FIG. 34, therefore, the effect of trackeccentricity can be canceled out, reducing a normal positioning errorwith respect to the target track center.

According to the present invention, as described above, tracks areformed in advance on a magnetic disk by impression, and wobbled marks, agray code, and other servo marks, and also clock marks, sector numbers,and track numbers are formed in advance on the magnetic disk byimpression. When the magnetic disk with the impressed marks is assembledin a casing (described later), it is unavoidable to introduce aneccentricity of about 50 μm. For accurately recording and reproducingdata, it is preferable to hold a positional error between a track andthe magnetic head to about 1 μm.

For example, a magneto-optical disk of the sampled servo type having adiameter of 130 mm which is defined by ISO-10089(B) has 1367 servoregions per revolution (circumference) of the disk, and amagneto-optical disk of the sampled servo type having a diameter of 90mm which is defined by ANSI-X3.213-1993 has 1472 servo regions perrevolution (circumference) of the disk. When these disks are rotated at60 Hz, the servo data are sampled at a sampling rate of 80 kHz to 88kHz, thereby producing a position signal having a band of 40 kHz orless.

Tracking servo control for an optical head used to record data on andreproduce data from a magneto-optical disk is simply carried out byactuating a small objective lens for applying a laser beam to themagneto-optical disk with a voice coil. Consequently, it is possible toprovide a tracking servo system having a gain of 1 substantially at 30kHz as indicated by the broken-line curve in FIG. 36, for example. Whenthe rotational frequency of the disk is 60 Hz, its gain becomes about500 times. Therefore, even if there is an eccentricity of 50 μm, afollow-up error can be held to about 0.1 μm.

In the magnetic disk device to which the present invention is applied,tracking control is carried out by angularly moving an arm which holds amagnetic head and is rotatably supported by a ball bearing. Therefore,the mass of an assembled arm and head to be actuated is much larger thanwith an optical head, and suffers mechanical resonance at a frequency inthe vicinity of 10 kHz.

Therefore, if the gain of the tracking servo system in the magnetic diskdevice, as indicated by the solid-line curve in FIG. 36, were to beincreased as a whole up to the position indicated by the broken-linecurve in FIG. 36, then oscillation would take place in the vicinity ofthe mechanical resonant frequency. For this reason, the gain of thetracking servo system cannot be increased in its entirety.

If the gain of the tracking servo system were increased in its entirety,then since the gain in a high-frequency range would also be increased,the sampling frequency for the servo data would have to be increasedaccording to the Nyquist's theorem. This would mean an increase in thenumber of servo data per track, and a corresponding reduction in therecording capacity of the disk.

Conversely, if the gain of the tracking servo system were set to themagnitude indicated by the solid-line curve in FIG. 36, since only again of about 50 times would be produced at the rotational frequency of60 Hz, the error of 50 μm would be reduced to only at most about 1 μm.

According to the present embodiment, however, a feed-forward signal isadded to a normal tracking error signal at the rotational frequency of60 Hz as described above. As a result, the apparent gain of the trackingservo system is locally increased at the frequency of 60 Hz as shown inFIG. 37. Because a gain of about 10 times can be obtained by thefeed-forward signal, the residual error of 1 μm due to the closed loopcan be reduced to 0.1 μm. Therefore, at least at the frequency of 60 Hz,it is possible to achieve a gain of 500 times, and the error of 50 μmcan be reduced to 0.1 μm.

By increasing the gain only in the vicinity of the rotational frequencyrather than increasing the gain as a whole, the frequency at which thegain becomes 1 can be reduced by about one figure as compared withincreasing the gain as a whole. Specifically, the frequency is 30 kHz inthe case of the broken-line curve shown in FIG. 36, but the frequency is3 kHz in the case of the solid-line curve shown in FIG. 37.

The sampling frequency required to reproduce positional information upto 3 kHz is at least 6 kHz according to the Nyquist's theorem. However,since this Nyquist's frequency is a frequency beyond which theinformation would be lost, a sampling frequency which is 5 through 10times the above sampling frequency is required from a practicalviewpoint. Therefore, the practical sampling frequency is 6 kHz×10÷60Hz=1000 (regions/circumference), and hence 1000 servo data regions maybe sufficient per circumference. An experiment indicated that goodpositioning characteristics would be obtained even when the number ofservo data regions per circumference was 840 or 420.

The aspect of detecting an off-track condition with respect to thetracking servo unit 10-7 shown in FIG. 1 will be described below.

FIG. 38 shows an embodiment of a detector for detecting an off-trackcondition. A window comparator 70-1 is supplied with a tracking errorsignal outputted from the track position error detector 50-23 shown inFIG. 21, for example. The window comparator 70-1 is also supplied with areference voltage outputted from a reference voltage generator 70-2. Thereference voltage includes a reference voltage as an upper threshold ofa window and a reference voltage as a lower threshold of the window.

The window comparator 70-1 compares the tracking error signal with thetwo thresholds, and outputs a detected signal to a determining circuit70-3 if the level of the tracking error signal is higher than the upperthreshold or lower than the lower threshold. The determining circuit70-3 determines whether a recording operation is to be interrupted ornot based on the inputted signal, and outputs the result ofdetermination to the recorder 10-9 shown in FIG. 1. The recorder 10-9interrupts the recording operation when supplied with the signal fromthe determining circuit.

A detailed determining process of the window comparator 70-1 and thedetermining circuit 70-3 will be described below with reference to aflowchart shown in FIG. 39.

First, the window comparator 70-1 determines in a step S70-1 whether thetracking error signal exists in a window or not. If the tracking errorsignal exceeds the range of the window, then a variable N is set to thenumber of times that the level of the tracking error exceeds the windowrange in a step S70-2. Therefore, the variable N represents the numberof times that the level of the tracking error exceeds the window range.

Then, control proceeds to a step S70-3 in which the number of successivetimes that the level of the tracking error exceeds the window range isstored. Specifically, the tracking error signal is sampled each time awobbled mark arrives (at the segment period), and when the trackingerror signal exceeds the window ranges in successive segments, thenumber of times that it exceeds the window range is stored. Then, a stepS70-4 determines whether or not the stored number of successive times is3 or more. If not 3 in succession, control goes to a step S70-5 whichdetermines whether the tracking error signal has exceeded the windowrange in three out of the four samplings in the past. If NO in the stepS70-5, then control goes to a step S70-6. If an end is not instructed,then control returns to the step S70-1, and the above process isrepeated.

If the stored number of successive times is 3 or more in the step S70-4,or if the tracking error signal has exceeded the window range in threeout of the four samplings in the past in the step S70-5, then controlgoes to a step S70-7 in which a pulse is outputted to stop the recordingoperation. The pulse is supplied to the recorder 10-9 shown in FIG. 1,and the recorder 10-9 stops the recording operation at the time it issupplied with the pulse. After the step S70-7, the step S70-6 is carriedout.

Since the magnetic disk of this embodiment has servo data recordingregions to produce positional data at a high frequency of 25 kHz, therecording operation is stopped only when the positional data outside ofthe detecting window are produced at a predetermined frequency orhigher.

It would theoretically be possible to stop the recording operationimmediately when the tracking error signal exceeds the window range onlyonce. In this case, if the window range were reduced, the magnetic headwould be prevented from moving to an adjacent track and from recordingdata in the adjacent track upon application of a large shock to themagnetic disk device. If, however, the window range were reducedexcessively, the recording operation would be stopped immediately evenwhen small noise would be produced, resulting in a reduction in thethroughput. If the window range were increased excessively, then wheninverse noise is produced causing the magnetic head to move to anadjacent track, such a condition would not be detected, and data wouldbe recorded in error on the adjacent track.

Therefore, as described above, it is preferable to stop the recordingoperation when an off-track condition is detected at a certainfrequency.

The window has equal positive and negative widths from a referenceposition as a center. If each width (1/2 width of the window) from thereference position of the window is 0.75 μm (which can correspond to thelevel of the tracking error and a relative positional deviation of themagnetic head from the reference position of a track), then an errordetection probability at the time a shock of 10 G, for example, isapplied may be held to 10⁻³ or less. The probability that the recordingoperation can be stopped while an off-track quantity is 0.95 μm or lessat the time a shock of 100 G is applied can be 95% or higher.

The reasons for the above probability will be described below.

It is assumed that any unbalanced condition between opposite sides ofthe center of rotation of the arm on which the magnetic head is mountedis 0.1 gcm or less, the sampling frequency for wobbled marks is 25 kHz,and the S/N ratio of the positional signal is 31 dB (if the track widthis 5 μm and a noise-induced deviation is 0.07 μm, then their ratio is 31dB).

It is also assumed that the arm has an inertia of 1.06×10³ gmm² and alength r of 36 mm. FIGS. 40A and 40B show the results of a simulation atthe time a shock of 10 G is applied while the unbalanced condition ofthe arm is 0.1 gcm (FIGS. 40A and 40B illustrate conditions when shocksof 10 G and 100 G are applied). As can be seen from FIGS. 40A and 40B,an off-track condition of 0.12 μm to one side (to the left or right) isproduced. It is assumed that an error can be detected in an interval inwhich the off-track condition is 0.1 μm or greater, the interval havinga time period of about 1.8 ms (45 samples).

A maximum off-track condition caused when the shock of 10 G is appliedis 0.6 μm. The probability of an error detection is calculated on theassumption that an off-track condition of 0.6 μm is produced during aperiod of 1.8 ms (45 samples). When the S/N ratio of the positionalsignal is 31 dB, the probability that the arm is observed as beingdisplaced 0.15 μm or more to one side from an actual position is1.62×10⁻². Therefore, the probability that three or more out ofsuccessive four samples are detected in error as being outside of thewindow (within 0.75 μm) while under an off-track condition of 0.6 μm is1.68×10⁻⁵. Since the probability that three or more out of successivefour samples in this interval (45 samples) is about 40 times the aboveprobability, i.e., about 7×10⁻⁴, the probability of an error detectionis 10⁻³ or less.

If the arm has an unbalanced condition of 0.1 gcm, then when a shock of10 G is applied thereto as shown in FIG. 40A, the arm is subjected to anoff-track condition caused after the application of the shock as shownin FIG. 40B. As shown in FIG. 40B, an off-track condition of ±1.2 μmoccurs in excess of the window range (±0.76 μm), and it can be seen thatit is necessary to stop the recording operation.

FIG. 41 shows on an enlarged scale a response immediately after a shockhas been applied. It can be understood from FIG. 41 that in an intervalin which an off-track condition ranges from 0.7 μm to 0.9 μm, themagnetic head moves at a speed of about 0.03 μm/sampling. Actually,since the path and speed of movement of the head vary due to noise, itis assumed that the head moves at a speed of 0.04 μm/sampling in theworst case.

FIG. 42 shows the manner in which the magnetic head is shifted off trackwhen a shock of 100 G is applied. While it has been described that anoff-track condition of 0.95 μm may be detected, it is preferable todetect an off-track condition of 0.91 μm in FIG. 42 in view of adeviation (at most 1 sample) of the position detecting timing. Assumingthat noise has a normal distribution of σ=0.07 μm, when the magnetichead moves along a path shown in FIG. 42, the probability that three ormore out of four successive samples fall outside of the window (within±0.75 μm) up to the off-track condition of 0.91 μm is 95.1%.

It follows from the above analysis that even when the magnetic headmoves along a path other than the path shown in FIG. 42 (even when theposition detection timing is incorrect), an off-track condition of 0.95μm or smaller can be detected with a probability of 95% or higher.

Since the detection ratio up to the off-track condition of 0.95 μm shownin FIG. 42 is 99.7%, the detection of an off-track condition can beexpected within 0.99 μm in the worst case.

FIG. 43 shows a response to a shock of 100 G in a simulation in whichthe S/N ratio is 31 dB and noise is added. In FIG. 43, the broken-linecurve represents an off-track quantity, and the solid-line curverepresents an observed position. After the off-track quantity exceeds awindow threshold of 0.75 μm and becomes 0.9 μm at the fourth sample, anoff-track deviation is detected, and a recording operation can bestopped at the time the off-track quantity becomes 0.95 μm or less.

By thus detecting a shock from the tracking error signal, it is possibleto detect a shock and stop a recording operation much faster than byproviding a piezoelectric element or the like in the magnetic diskdevice for detecting shocks.

The aspect of the reproducer 10-8 shown in FIG. 1 will be describedbelow.

A three-value level detecting process using three thresholds, -2, 0, +2,for example, may be relied on to decode data reproduced from a magneticdisk on which data and various marks are recorded. Such a process isadvantageous in that a circuit arrangement required is simple, butdisadvantageous in that the detecting capability is relatively low.

In view of its drawbacks, such a decoding process, though applicable todecode data in data regions, is not suitable for regions such as an IDregion of a sector (the gray code 20-72, the sector number 20-41a, andthe track numbers 20-41b1, 20-41b2) where after an ID has been decoded,it is to be quickly determined whether data are to be read from orwritten in the sector.

There has been known a Wood's algorithm as a process for recording dataon and reproducing data from a magnetic disk using a partial responseprocess, as described in "Viterbi Detection of Class IV Partial Responseon a Magnetic Recording Channel", IEEE TRANSACTIONS ON COMMUNICATIONS,VOL. COM-34, NO. 5, MAY 1986, for example.

According to the Wood's algorithm described in the above literature, aViterbi algorithm is simplified in accord with a pair of partialresponses (1, -1) equivalent to a partial response class IV (partialresponses (1, 0, -1)), and decoded data of an improved error ratio canbe obtained by determining whether a survival path pattern is any one ofthree patterns as shown in FIGS. 44A, 44B, 44C:

status <-1> →status <-1> and status <-1> →status <+1> (FIG. 44A);

status <-1> →status <-1> and status <+1> →status <+1> (FIG. 44B); and

status <+1> →status <+1> and status <+1> →status <-1> (FIG. 44C).

The three survival path patterns are represented by three two-charactersymbols: →↑ (upward divergence), →→ (parallel), and ←↓ (downwarddivergence).

According to the Wood's algorithm, when an upward divergence →↑ or adownward divergence ←↓ appears as a survival path pattern, a path from alocation k where it appears to a location p which precedes the locationk and in which a divergence has appeared can be determined, and data canbe decoded by repeating such a process.

FIG. 45 shows an arrangement of a reproducing circuit 80-80 for decodingdata from a magnetic disk (having a format shown in FIG. 2) using theWood's algorithm, and detecting an error of the decoded data.

Data from the magnetic disk are inputted to a processor 80-10 or 80-20in which even-series samples or odd-series samples are individuallyprocessed. Thereafter, the data are decoded into an original sequence bya combining circuit 80-2 based on the timing of a switching signaloutputted from a switching circuit 80-1, and outputted.

In FIG. 45, the processor 80-10 for processing an even series of samplesis shown in detail. The processor 80-20 for processing an odd series ofsamples is of the same arrangement.

In the processor 80-10, data from the magnetic disk are supplied to asubtractor 80-12 and a register 80-13b through a switch 80-11 which isturned on and off at the timing of even-series samples/odd-seriessamples by a switching signal (even/odd⁻¹ (indicated by odd with anoverbar in FIG. 45)) outputted from a switching circuit 80-1. Thesubtractor 80-12 and the register 80-13b are supplied with even-seriessamples of data from the magnetic disk.

The register 80-13b stores a sample value yp in a preceding divergencelocation, and the subtractor 80-12 subtracts the value yp stored in theregister 80-13b from the supplied even-series samples (even-seriessamples of data from the magnetic disk 10-2), i.e., calculates (yk-yp),and outputs the result to a comparator 80-14.

The comparator 80-14 effects calculations as shown in Tables 2 and 3 onthresholds +2, 0, -2, the output signal (yk-yp) from the subtractor80-12, and β stored in a register 80-13a, and outputs output data shownin Tables 2 and 3 based on the calculated result. Details of suchcalculations will be described in detail later on with reference to FIG.46.

As shown in FIG. 65 or 66, D outputted from the comparator 80-14 takes avalue of +1 or -1. If a preceding divergence is an upward divergence(→↑), then β is set to 1, and if a preceding divergence is a downwarddivergence (←↓), then β is set to (-1). Therefore, β is indicative ofthe type of a preceding divergence (whether a preceding divergence is anupward or downward divergence).

A register 80-15 counts a PLL clock outputted from a PLL (not shown),and stores a count k (a sampling time). A register 80-16 stores thecount k from the register 80-15 as a value p (a time at which apreceding divergence has occurred) according to an updating command(UPDATE) outputted from the comparator 80-14. A selector 80-17 selectsthe value p stored in the register 80-16 or the value k stored in theregister 80-15 depending on a selection command (p or k) outputted fromthe comparator 80-14.

A RAM 80-18 writes output data (DATA) from the comparator 80-14 in amemory cell with the output signal (p or k) from the selector 80-17being used as a write address. A counter 80-19 counts up data written inthe RAM 80-18 based on a reference clock outputted from a circuit (notshown). When the writing of data in all memory cells is completed, theRAM 80-18 delivers the data in all memory cells to the combining circuit80-2 based on the count of the counter 80-19. The combining circuit 80-2returns the even-series samples from the processor 80-10 and theodd-series samples from the processor 80-20 back to their originalsequence, and outputs them based on the switching signal (even/odd⁻¹)from the switching circuit 80-1.

With the arrangement shown in FIG. 45, no squaring unit is required andone adder and two comparators are sufficient for Viterbi decoding ofdata. However, the RAM 80-18 is needed for storing paths.

A shift register calculating circuit 80-3 effects Viterbi decoding basedon the Wood's algorithm and at the same time carries out CRCcalculations, using the switching signal (even/odd⁻¹) from the switchingcircuit 80-1, the updating command (UPDATE) and the output data (DATA)from the processor 80-10, and the updating command (UPDATE) and theoutput data (DATA) from the processor 80-20.

An operation of the circuit shown in FIG. 45 in response to a certainsignal inputted thereto will be described below with reference to atiming chart shown in FIG. 46.

When a signal (input waveform) shown in FIG. 46 is inputted to thereproducer 80-80 shown in FIG. 45, the comparator 80-14 operates asshown in FIGS. 65 and 66. It is assumed that yp and β have initialvalues: yp=-2, β=-1. <When k=0: input yk=y0=1.6; yp=-2; β=-1>

Since yk-yp=1.6-(-2)=3.6 >2, the input corresponds to a conditionpattern F shown in FIG. 66. Because it is an upward divergence, β of theregister 80-13a is updated to +1 according to the table shown in FIG.66, p (a time at which a preceding divergence has occurred) is updatedto p=k=0 with the register 80-16, and yp (sample value at the time atwhich a preceding divergence has occurred) is set to yp=y0=1.6 with theregister 80-13b. <When k=1: input yk=y1=0.2; yp=1.6; β=+1; p=0>

Since -2<yk-yp=0.2-1.6=-1.4≦0, the input corresponds to a conditionpattern B shown in FIG. 65. Because it is a parallel path, β of theregister 80-13a and yb of the register 80-13b remain as they are, thevalue k (=1) stored in the register 80-15 is selected by the selector80-17, and data (RAM data) 0 are written at an address k (=1) in the RAM80-18 (the logic of data at k=1 is set to 0 and the data decoded).

<When k=2: input yk=y2=-0.2; yp=1.6; β=+1; p=0>

Since -2<yk-yp=-0.2-1.6=-1.8≦0, the input corresponds to a conditionpattern B shown in FIG. 65. Because it is a parallel path, β of theregister 80-13a and yp of the register 80-13b remain as they are, thevalue k (=2) stored in the register 80-15 is selected by the selector80-17, and data 0 are written at an address k (=2) in the RAM 80-18 (thelogic of data at k=2 is set to 0 and the data decoded).

<When k=3: input yk=y3=2.0; yp=1.6; β=+1; p=0>

Since yk-yp=2.0-1.6=0.4>0, the input corresponds to a condition patternC shown in FIG. 65. Because it is an upward divergence, the precedingcandidate yp is defeated by the present value yk (yp<yk). Though it isdetermined as an upward divergence (β=+1) at k=0 (p=0), since an upwarddivergence (β=+1) occurs at present (k=3), the preceding divergence wasa parallel path of an upward divergence (if an upward transitionoccurred at k=0, then a path would be discrete at k=3).

The value p (=0) of the register 80-16 is selected by the selector80-17, and data 0 are written at an address p (=0) in the RAM 80-18 (thelogic of data at k=0 is set to 0 and the data decoded). β in theregister 80-13a is set to +1, the stored value p of the register 80-16is updated with the stored value k of the register 80-15 so as to bep=k=3, and the stored value yp of the register 80-13b is set toyp=y3=2.0.

<When k=4: input yk=y4=0.2; yp=2.0; β=+1; p=3>

Since -2<yk-yp=0.2-2.0=-1.8≦0, the input corresponds to a conditionpattern B shown in FIG. 65. Because it is a parallel path, β and ypremain as they are, k (=4) is selected, and data 0 are written at anaddress k (=4) in the RAM 80-18 (the logic of data at k=4 is set to 0and the data decoded).

<When k=5: input yk=y5=-0.4; yp=2.0; β=+1; p=3>

Since yk-yp=-0.4-2.0=-2.4≦-2, the input corresponds to a conditionpattern A shown in FIG. 65. Because it is a downward divergence, thepreceding candidate is correct (an upward transition occurred of anupward divergence at k=3 (p=3)). Therefore, data 1 are written at anaddress p (=3) in the RAM 80-18 (the logic of data at k=3 is set to 1and the data decoded). β is set to -1, p is updated to p=k=5, and yp isset to yp=y5=-0.4.

<When k=6: input yk=y6=-0.2; yp=-0.4; β=-1; p=5>

Since 0<yk-yp=-0.2-(-0.4)=0.2≦+2, the input corresponds to a conditionpattern E shown in FIG. 66. Because it is a parallel path, β and ypremain as they are, k is selected, and data 0 are written at an addressk (=6) in the RAM 80-18 (the logic of data at k=6 is set to 0 and thedata decoded).

<When k=7: input yk=y7=-2.0; yp=-0.4; β=-1; p=5>

Since yk-yp=-2.0-(-0.4)=-1.6≦0, the input corresponds to a conditionpattern D shown in FIG. 66. Because it is a downward divergence, thepreceding candidate is defeated. As a parallel transition, rather than adownward transition, occurred at k=5 (p=5), data 0 are written at anaddress p (=5) in the RAM 80-18 (the logic of data at k=5 is set to 0and the data decoded). β is set to -1, p is updated to p=k=7, and yp isset to yp=y7=-2.0.

<When k=8: input yk=y8=0.2; yp=-2.0; β=-1; p=7>

Since yk-yp=0.2-(-2.0)=2.2>+2, the input corresponds to a conditionpattern F shown in FIG. 66. Because it is an upward divergence, thepreceding data are correct. Therefore, as a downward transition occurredat k=7 (p=7), data 1 are written at an address p (=7) in the RAM 80-18(the logic of data at k=7 is set to 1 and the data decoded). β is set to+1, and yp is set to yp=y8=0.2 (FIG. 46).

Data are subsequently decoded based on the Wood's algorithm in the samemanner as described above, and the decoded data are successively writtenin the RAM 80-18.

As shown in FIG. 47, the RAM 80-18 comprises, for example, a pluralityof memory cells D₀ through D_(n) each having a 1-bit capacity, anaddress decoder 80-31, and a plurality of write control lines 80-32₋₀through 80-32_(-n) connected respectively to the memory cells D₀ throughD_(n). All of the memory cells D₀ through D_(n) are supplied with data(DATA) from the comparator 80-14 shown in FIG. 45.

The address decoder 80-31 is supplied with write addresses A₀ throughA_(n) from the selector 80-17 shown in FIG. 45, decodes the writeaddresses A₀ through A_(n), and supplies 1-bit signals as write signalsto memory cells D₀ through D_(n) for thereby writing the data (DATA)from the comparator 80-14 in prescribed memory cells.

After the writing of data in all the memory cells D₀ through D_(n) iscompleted, the data stored in all the memory cells D₀ through D_(n) aresimultaneously outputted to the combining circuit 80-2. Therefore, allthe data are read out at this time.

The data reading timing is compared with the conventional process (e.g.,the process described in the above literature of Wood). Timing charts ofthe data reading processes are shown in FIGS. 48A and 48B. FIG. 48B is atiming chart of the data reading process carried out by the reproducer80-80. When a write enable signal for writing data in the RAM 80-18becomes active, the ID portion is decoded. When the writing of all thedata is finished, a read enable signal for reading data from the RAM80-18 becomes active, and the sequence enters a data region forsimultaneously reading all the data.

Comparison with the conventional process shown in FIG. 48A indicatesthat a delay time after the writing of data is finished and until thereading of data from the RAM 80-18 is finished is greatly reduced. Eachof the memory cells D₀ through D_(n) can easily be implemented by a1-bit flip-flop, for example, with a write control signal inputted insynchronism with a clock.

If the reproducer 80-80 is used for reproducing data from the IDrecording region 20-41H, for example, then since it is possible todetermine quickly whether a sector number and a track number are desirednumbers or not, data can be processed without providing any essentialaccessing gap between ID and data portions.

Inasmuch as each of sector numbers and track numbers, for example, arecomposed of at most several bytes, all the bits may be outputted atonce, which may amount to several tens bits. Consequently, the abovearrangement is sufficiently practical.

All the bits may not be read from the RAM 80-18 at once, but lumps of 8bits, for example, may be read. With such a modification, the timerequired after the data have started to be read from the RAM 80-18 anduntil they have fully been read from the RAM 80-18 can be reduced to1/8. This process offers the same advantages as those of the aboveprocess.

To sector numbers and track numbers, there are normally added an errordetecting code such as a CRC (Cyclic Redundancy Check) code, forexample.

If a generator polynomial G(x) which is expressed by:

    G(x)=x.sup.16 +x.sup.12 +x.sup.5 +1                        (80-1)

is used for a CRC code, then data per bit length BL are divided by thegenerator polynomial G(x)=x¹⁶ +x¹² +x⁵ +1, and the remainder is added tothe end of the data (e.g., sector ID).

In the shift register calculating circuit 80-3 of the reproducer 80-80shown in FIG. 45, the data are decoded (Viterbi decoding) and CRCcalculations are effected thereon, using the switching signal(even/odd⁻¹) from the switching circuit 80-1, the updating command(UPDATE) and the output data (DATA) from the processor 80-10, and theupdating command (UPDATE) and the output data (DATA) from the processor80-20.

The updating command (UPDATE) and the output data (DATA) outputted fromthe comparator 80-14 of the processor 80-10 which processes even-seriessamples are indicated with "₋₋ even" added to the ends of theircharacter trains to show that they are signals corresponding toeven-series samples. The updating command (UPDATE) and the output data(DATA) outputted from the comparator of the processor 80-20(corresponding to the comparator 80-14 of the processor 80-10) whichprocesses odd-series samples are indicated with "₋₋ odd" added to theends of their character trains to show that they are signalscorresponding to odd-series samples.

As shown in FIG. 49, if the largest degree of a generator polynomial inCRC calculations is indicated by J, then the shift register calculatingcircuit 80-3 comprises a parallel load/serial shift register composed offour a- to d-series serial shift registers having cascaded (J+2)flip-flops D_(a-1) through D_(aj) with (J+1) selectors S_(a0) throughS_(aj) connected therebetween, cascaded (J+2) flip-flops D_(b-1) throughD_(bj) with (J+1) selectors S_(b0) through S_(bj) connectedtherebetween, cascaded (J+2) flip-flops D_(c-1) through D_(cj) with(J+1) selectors S_(c0) through S_(cj) connected therebetween, andcascaded (J+2) flip-flops D_(d-1) through D_(dj) with (J+1) selectorsS_(d0) through S_(dj) connected therebetween.

The flip-flops D_(a-1) through D_(aj), D_(b-1) through D_(bj), D_(c-1)through D_(cj), D_(d-1) through D_(dj) latch inputted data in timedrelationship to a supplied clock (not shown). The selectors S_(a0)through S_(aj), S_(b0) through S_(bj), S_(c0) through S_(cj), S_(d0)through S_(dj) selects and outputs one of inputted three signals basedon the switching signal (even/odd⁻¹ (indicated by odd with an overbar inFIG. 49)) outputted from the switching circuit 80-1, UPDATE₋₋ even andDATA₋₋ even from the processor 80-10, and UPDATE₋₋ odd and DATA₋₋ oddfrom the processor 80-20.

In this embodiment, the generator polynomial in CRC calculations is G(x)represented by the equation (80-1) given above. Therefore, J is 16.

In the shift register calculating circuit 80-3, (XOR) gates 80-41athrough 80-41d are connected between the flip-flops D_(a0), D_(b0),D_(c0), D_(d0) and the selectors S_(a1), S_(b1), S_(c1), S_(d1), XORgates 80-42a through 80-42d are connected between the flip-flops D_(a5),D_(b5), D_(c5), D_(d5) and the selectors S_(a6), S_(b6), S_(c6), S_(d6),and XOR gates (not shown) are connected between the flip-flops D_(a12),D_(b12), D_(c12), D_(d12) and the selectors S_(a13), S_(b13), S_(c13),S_(d13). Output signals from the respective flip-flops D_(a16), D_(b16),D_(c16), D_(d16) are inputted (fed back) to the XOR gates 80-41a through80-41d.

In the shift register calculating circuit 80-3, output signals from theXOR gates 80-41a through 80-41d are inputted respectively to the XORgates 80-42a through 80-42d, and also to the XOR gates connected betweenthe flip-flops D_(a12), D_(b12), D_(c12), D_(d12) and the selectorsS_(a13), S_(b13), S_(c13), S_(d13)

Therefore, each of the four a- to d-series serial shift registers of theshift register calculating circuit 80-3 is of the same arrangement asthat which has selectors in a CRC decoder (not shown) for effecting CRCcalculations corresponding to the generator polynomial according to theequation (80-1) and two flip-flops and one selector in a front stage ofthe CRC decoder.

Each of the four a- to d-series serial shift registers of the shiftregister calculating circuit 80-3 effects CRC calculations based on thegenerator polynomial G(x) according to the equation (80-1).

A circuit which is similar to the shift register calculating circuit80-3 but devoid of all the XOR gates selects a surviving series ofserial shift registers, i.e., a path, and decodes data by Viterbidecoding while combining even-series samples and odd-series samples,based on UPDATE₋₋ even and DATA₋₋ even from the processor 80-10 andUPDATE₋₋ odd and DATA₋₋ odd from the processor 80-20.

The circuit which is devoid of all the XOR gates in the shift registercalculating circuit 80-3, therefore, decodes reproduced datasuccessively (in the order of samples) by Viterbi decoding, and outputsthe decoded data.

The shift register calculating circuit 80-3 is supplied with UPDATE₋₋even and DATA₋₋ even from the processor 80-10 or UPDATE₋₋ odd and DATA₋₋odd from the processor 80-20, and the switching signal (even/odd⁻¹) fromthe switching circuit 80-1 according to the tables shown in FIGS. 65 and66.

If the switching signal (even/odd⁻¹) from the switching circuit 80-1 isof logic 1 (H level), then the data are processed based on UPDATE₋₋ evenand DATA₋₋ even from the processor 80-10. If the switching signal(even/odd⁻¹) from the switching circuit 80-1 is of logic 0 (L level),then the data are processed based on UPDATE₋₋ odd and DATA₋₋ odd fromthe processor 80-20.

More specifically, in the shift register calculating circuit 80-3, asignal generator (not shown) generates four signals (input₋₋ a, input₋₋b, input₋₋ c, input₋₋ d) indicated by respective equations given below,from the switching signal (even/odd⁻¹) from the switching circuit 80-1,UPDATE₋₋ even and DATA₋₋ even from the processor 80-10, and UPDATE₋₋ oddand DATA₋₋ odd from the processor 80-20.

input₋₋ a=(even/odd⁻¹ =1*UPDATE₋₋ even+(even/odd⁻¹ =0)*UPDATE₋₋ odd

input₋₋ b=(even/odd⁻¹ =1*UPDATE₋₋ even

input₋₋ c=(even/odd⁻¹ =0*UPDATE₋₋ odd

input₋₋ d=0

where * indicates ANDing and +ORing. (even/odd⁻¹ =1) becomes logic 1 ifeven/odd⁻¹ is logic 1 (at the timing of even-series samples), andbecomes logic 0 if even/odd⁻¹ is logic 0 (at the timing of odd-seriessamples). (even/odd⁻¹ =0) becomes logic 0 if even/odd⁻¹ is logic 1, andbecomes logic 1 if even/odd⁻¹ is logic 0.

Therefore, the signal input₋₋ b is of the same value as UPDATE(UPDATE₋₋even) outputted from the processor 80-10, which is effective only at thetiming of even-series samples, and the signal input₋₋ c is of the samevalue as UPDATE(UPDATE₋₋ odd) outputted from the processor 80-20, whichis effective only at the timing of odd-series samples. The signalinput₋₋ a is of the same value as UPDATE(UPDATE₋₋ even) outputted fromthe processor 80-10 at the timing of even-series samples, and is of thesame value as UPDATE(UPDATE₋₋ odd) outputted from the processor 80-20 atthe timing of odd-series samples. The signal input₋₋ d is 0 at alltimes.

The four signals input₋₋ a, input₋₋ b, input₋₋ c, input₋₋ d are inputtedrespectively to the first flip-flops D_(a-1) through D_(d-1) of theshift register calculating circuit 80-3 (FIG. 49).

The signals input₋₋ a, input₋₋ b, input₋₋ c, input₋₋ d inputtedrespectively to the first flip-flops D_(a-1) through D_(d-1) aresuccessively latched in next flip-flops through respective selectors intimed relationship to the clock.

The selectors S_(aj), S_(bj), S_(cj), S_(dj) (i=0, 1, . . . J (J=16 inthis embodiment as described above)) output signals out₋₋ a, out₋₋ b,out₋₋ c, out₋₋ d, respectively, according to the following equationswhere signals from previous stages of the a- through d-series shiftregisters:

out₋₋ a=(even/odd⁻¹ =1)*(UPDATE₋₋ even=1)* (DATA₋₋ even=0)*in₋₋c+(even/odd⁻¹ =1)* ((UPDATE₋₋ even=1)*(DATA₋₋ even=0))⁻¹ * in₋₋a+(even/odd⁻¹ =0)*(UPDATE₋₋ odd=1)* (DATA₋₋ odd=0)*in₋₋ b+(even/odd⁻¹=0)* ((UPDATE₋₋ odd=1)*(DATA₋₋ odd=0))⁻¹ *in₋₋ a

out₋₋ b=(even/odd⁻¹ =1)*(UPDATE₋₋ even=1)* (DATA₋₋ even=0)*in₋₋d+(even/odd⁻¹ =1)* ((UPDATE₋₋ even=1)*(DATA₋₋ even=0))⁻¹ * in₋₋b+(even/odd⁻¹ =0)*(UPDATE₋₋ odd=1)* (DATA₋₋ odd=1)*in₋₋ a+(even/odd⁻¹=0)* ((UPDATE₋₋ odd=1)*(DATA₋₋ odd=1))⁻¹ *in₋₋ b

out₋₋ c=(even/odd⁻¹ =1)*(UPDATE₋₋ even=1)* (DATA₋₋ even=1)*in₋₋a+(even/odd⁻¹ =1)* ((UPDATE₋₋ even=1)*(DATA₋₋ even=1))⁻¹ * in₋₋c+(even/odd⁻¹ =0)*(UPDATE₋₋ odd=1)* (DATA₋₋ odd=0)*in₋₋ d+(even/odd⁻¹=0)* ((UPDATE₋₋ odd=1)*(DATA₋₋ odd=0))⁻¹ *in₋₋ c

out₋₋ d=(even/odd⁻¹ 1)*(UPDATE₋₋ even=1)* (DATA₋₋ even=1)*in₋₋b+(even/odd⁻¹ =1)* ((UPDATE₋₋ even=1)*(DATA₋₋ even=1))⁻¹ * in₋₋d+(even/odd⁻¹ =0)*(UPDATE₋₋ odd=1)* (DATA₋₋ odd=1)*in₋₋ c+(even/odd⁻¹=0)* ((UPDATE₋₋ odd=1)*(DATA₋₋ odd=1))⁻¹ *in₋₋ d

where ()⁻¹ indicates negation of what is contained in (). Therefore, ()⁻¹ is logic 0 if the logic in () is 1, and logic 1 if the logic in ( )is 0.

According to the above equations, a surviving series (correct path) ofserial shift registers is selected from UPDATE₋₋ even and DATA₋₋ evenfrom the processor 80-10 and UPDATE₋₋ odd and DATA₋₋ odd from theprocessor 80-20, and the data latched in the flip-flops of the selectedseries of shift registers are copied into the flip-flops of anotherseries of shift registers and Viterbi-decoded.

Simultaneously in the shift register calculating circuit 80-3, outputsignals from the final flip-flops D_(a16) through D_(d16) of the a- andd-series serial shift registers and the flip-flops D_(a0) through D_(d0)thereof are XORed by the respective XOR gates 80-41a through 80-41d,whose output signals are inputted to the selectors S_(a1) through S_(d1)respectively.

The output signals from the XOR gates 80-41a through 80-41d and outputsignals from the flip-flops D_(a5) through D_(d5) of the a- and d-seriesserial shift registers are XORed by the respective XOR gates 80-42athrough 80-42d, whose output signals are inputted to the selectorsS_(a6) through S_(d6), respectively. The output signals from the XORgates 80-42a through 80-42d and output signals from flip-flops D_(a12)through D_(d12) (not shown) of the a- and d-series serial shiftregisters are XORed by XOR gates disposed between those flip-flopsD_(a12) through D_(d12) and flip-flops D_(a13) through D_(d13) (notshown). Output signals from those XOR gates are inputted to therespective selectors S_(a13) through S_(d13).

Therefore, the shift register calculating circuit 80-3 carries out CRCcalculations based on the generator polynomial according to the equation(80-1).

In order to Viterbi-decoding partial responses (1, 0, -1), a 2-bit codefor ending a trellis diagram (hereinafter referred to as a "trellis") isrequired at the end of a block of data (a bit series) to be decoded (abit series as a unit to be decoded). The 2-bit code is a code prior to aprecode, and 11 is generally added as such a 2-bit code to the end of ablock.

The 2-bit code for ending a trellis is not required for effecting CRCcalculations. In the shift register calculating circuit 80-3, therefore,when 2-bit data corresponding to a code (11) for ending a trellis arelatched respectively by the flip-flops D_(a-1) through D_(d-1) andD_(a0) through D_(d0) of the a- and d-series serial shift registers, theresult of CRC calculations is evaluated based on 16 bits latched in anyof the flip-flops D_(a1) through D_(a16), D_(b1) through D_(b16), D_(c1)through D_(c16), and D_(d1) through D_(d16).

Specifically, if 16 bits latched in any of the flip-flops D_(a1) throughD_(a16), D_(b1) through D_(b16), D_(c1) through D_(c16), and D_(d1)through D_(d16) are all 0, then the result of CRC calculations isevaluated such that the data contain no error, and if any one of the 16bits is not 0, then the result of CRC calculations is evaluated suchthat the data contain an error.

In the shift register calculating circuit 80-3, as described above, theXOR gates for XORing output signals from the cascaded flip-flops of thea- and d-series serial shift registers for carrying out a Viterbidecoding process are disposed between those flip-flops to effect CRCcalculations. Therefore, if a Jth-degree generator polynomial for a CRCcode is used, then a result of CRC calculations can be obtained within aJ-1 clock after the final bit of a block of data from the magnetic disk10-2 has been inputted to the reproducer 80-80 shown in FIG. 45.

Since Viterbi decoding and CRC calculations are simultaneously carriedout as shown in FIG. 50B, any time delay necessary for decoding data anddetecting an error can greatly be reduced.

Consequently, as compared with the conventional process shown in FIG.50A in which CRC calculations are carried out after data have beenViterbi-decoded, the gap between the ID and data portions of themagnetic disk (e.g., the distance between the ID recording region 20-41Hand the data recording region 20-41D or the distance between the graycode 20-71 and the ID recording region 20-41H as shown in FIG. 2) can bereduced for a larger capacity of the magnetic disk.

In the above description of the shift register calculating circuit 80-3,the generator polynomial for CRC according to the equation (80-1) hasbeen employed. However, the generator polynomial is not limited to theequation (80-1), but may be represented by another equation. Dependingon the generator polynomial that is used, the step number of flip-flopsof the shift register calculating circuit 80-3 may be increased orreduced, and the number and inserted position of XOR gates may bevaried.

The reproducer 80-80 is also applicable to decode not only the IDportion but also data in the data region (data recorded in the datarecording region 20-41D shown in FIG. 2).

The aspect of the recorder 10-9 shown in FIG. 1 will be described below.

FIG. 51 is a block diagram showing an entire arrangement of a magneticdisk device. The magnetic disk device is of the so-called externalsynchronous type (sample servo type) in which data are recorded on orrecorded data are reproduced from a magnetic disk 90-1 (that isformatted as shown in FIG. 2) on which clock marks have been recordedfor generating a clock.

The magnetic disk device has a playback head 90-11a for reproducing datafrom the magnetic disk 90-1, a playback amplifier 90-12 for amplifying asignal reproduced by the playback head 90-11a, a clock generator 90-13for generating a clock based on a reproduced signal amplified by theplayback amplifier 90-12 and corresponding to clock marks on themagnetic disk 90-1, and a data demodulator 90-14 for reproducing data orthe like from the reproduced signal from the playback amplifier 90-12using the clock from the clock generator 90-13.

The magnetic disk device also has a timing generator 90-15 for countinga clock from the clock generator 90-13 to control the clock generator90-13 and output a switching signal to switch between recording andplayback modes, a recording data generator 90-16 for converting inputteddata (corresponding to the recording signal inputted to the recorder10-9 shown in FIG. 1, and hereinafter referred to as "source data") intodata suitable for recording (hereinafter referred to as "recordingdata"), a pulse delay circuit 90-30 for delaying the recording data fromthe recording data generator 90-16, a recording head 90-11b forrecording the recording data delayed by the pulse delay circuit 90-30 onthe magnetic disk 90-1, a recording amplifier 90-18 for supplying acurrent based on the recording data delayed by the pulse delay circuit90-30 to the recording head 90-11b, and a delay time control circuit90-20 for controlling a delay quantity in the pulse delay circuit 90-30based on a position (hereinafter referred to as "head positioninformation") of the recording head 90-11b in the radial direction ofthe disk, from the data demodulator 90-14.

As described above with reference to FIGS. 17 and 18, the playback head90-11a comprises a so-called magnetoresistance-effect head (MR head) forachieving high-density recording, and the recording head 90-11bcomprises an ordinary magnetic head. The playback head 90-11a and therecording head 90-11b are spaced from each other by a distance L in thedirection in which they run with respect to the magnetic disk. Theplayback head 90-11a and the recording head 90-11b jointly constitute aso-called recording/playback-separated head 90-11.

On the magnetic disk 90-1 which is rotated at a constant angularvelocity (so-called zone bit recording with a clock frequency changedper zone) by a spindle motor (100-21 shown in FIG. 59), there areformed, as shown in FIG. 52A, radially successive clock marks 90-3(20-11 in FIG. 2) for generating a clock by partially removing amagnetic layer, for example, as by etching, between data segments 90-2(the data recording regions 20-41D in FIG. 2) which are regions forrecording data on concentric recording tracks. These clock marks 90-3are magnetized in one direction by a direct current, and provided inabout several hundred to one thousand locations (840 locations in theabove example) per circumference for generating a highly accurate clock.

The playback head 90-11a outputs a reproduced signal corresponding todata recorded in the data segments 90-2 and also outputs a reproducedsignal corresponding to the clock marks 90-3, and supplies thesereproduced signals through the playback amplifier 90-12 to the clockgenerator 90-13 and the data demodulator 90-14.

The clock generator 90-13 has the PLL circuit 50-30 described withreference to FIG. 21, and generates a clock based on the reproducedsignal corresponding to the clock marks 90-3.

More specifically, when the clock marks 90-3 magnetized in one direction(the rightward direction indicated by the arrows in FIG. 52A) by adirect current as shown in FIG. 52A are reproduced, a reproduced signalhaving an isolated waveform is reproduced by leading and trailing edgesof the clock marks 90-3 as shown in FIG. 52B. The timing generator 90-15counts the clock supplied from the clock generator 90-13, predicts aperiod in which the reproduced signal corresponding to the clock marks90-3 appears based on the past history, supplies a clock gate signalrepresentative of the predicted period to the clock generator 90-13, andgenerates a switching signal for switching between the recording andplayback modes as shown in FIG. 52D.

The clock generator 90-13 regards an isolated waveform appearing in aperiod in which a clock gate signal is produced, as a normal clock mark,updates the PLL phase so as to synchronize a positive-going edge of theclock with the peak of the isolated waveform corresponding to theleading edge, as shown in FIG. 52N, for example, and generates a clockkept in phase with the clock marks 90-3.

In the playback mode, the data demodulator 90-14 discriminates thereproduced signal (samples the level) at the times of positive-goingedges (hereinafter referred to as "data-present-point phase" of theclock generated by the clock generator 90-13, for example, anddemodulates (Viterbi-decodes, as described above with reference to FIGS.44 through 50) the signal to reproduce data. The data demodulator 90-14also reproduces head position information (e.g., the gray code 20-71,the track numbers 20-41b1, 20-41b2, etc. in FIG. 2) of the head 90-11 inthe radial direction of the disk based on the reproduced signal, andsupplies the head position information to the delay time control circuit90-20.

In the recording mode, the recording data generator 90-16 convertssource data into recording data synchronous with the clock generated bythe clock generator 90-13 according to a prescribed modulation processsuitable for recording (PR modulation as described above), and suppliesthe recording data synchronous with the clock to the pulse delay circuit90-30 and the delay time control circuit 90-20.

The pulse delay circuit 90-30 is controlled by the delay time controlcircuit 90-20 to delay recording data so as to compensate for a phasedeviation of data, to be recorded in the data segments 90-2, due to thedistance L between the playback head 90-11a and the recording head90-11b in the direction in which they run with respect to the disk, andalso to compensate for a positional deviation (hereinafter referred toas a "nonlinear bit shift") of magnetization reversal due to the patternof the recording data. The recording amplifier 90-18 amplifies thedelayed recording data, and supplies a current based on the recordingdata to the recording head 90-11b.

More specifically, as shown in FIG. 53, the delay time control circuit90-20 comprises an adder 90-21 for adding a constant C3 to the headposition information (track number) from the data demodulator 90-14, amultiplier 90-22 for multiplying an output signal from the adder 90-21by a constant C2, cascaded delay units 90-23a, 90-23b each for delayingthe recording data from the recording data generator 90-16 by one clock,an exclusive-OR (hereinafter referred to as "XOR") gate 90-24a forXORing the recording data from the recording data generator 90-16 andthe recording data delayed by the delay unit 50-23a, an XOR gate 90-24bfor XORing the recording data delayed by the delay unit 90-23a and therecording data delayed by the delay unit 90-23b, an AND gate 90-25 forANDing an output signal from the XOR gate 90-24a and an output signalfrom the XOR gate 90-24b, a selector switch 90-26 for selecting aconstant C1 or a constant 0 based on an output signal from the AND gate90-25, and an adder 90-27 for adding an output signal from the selectorswitch 90-26 and an output signal from the multiplier 90-22 to eachother.

The delay time control circuit 90-20 calculates the time differencebetween the data-present-point phase and a time at which the recordingcurrent is to be actually reversed based on the head positioninformation supplied from the data demodulator 90-14 and the recordingdata, and outputs a delay time indicating signal.

More specifically, if it is assumed that the head position informationsupplied from the data demodulator 90-14 is a track number N where thehead 90-11 is currently positioned, for example, then the adder 90-21adds the track number N and the constant C3 (corresponding to thedistance from the center of the disk to a radially innermost track), andthe multiplier 90-22 multiplies the sum from the adder 90-21 by theconstant C2. The multiplier 90-22 outputs a value proportional to thedistance (N+C3) from the disk center to the head 90-11 as a delay timeT1 for compensating for a phase deviation of the data due to thedistance L between the playback head 90-11a and the recording head90-11b in the direction in which they run, according to the followingequation (90-1):

    T1=(N+C3)×C2                                         (90-1).

The constants C2, C3 are of such a value as to satisfy T1=L/v where v isa speed of the head 90-11 at the time it is positioned on the trackwhose track number is N. Stated otherwise, the delay time T1 is equal toa time in which the magnetic disk moves by the distance L.

Each of the delay units 90-23a, 90-23b delays the recording data by oneclock. The XOR gates 90-24a, 90-24b XOR 2 adjacent bits of successive 3bits of the recording data. The AND gate 90-25 ANDs output signals fromthe XOR gates 90-24a, 90-24b. As a result, the AND gate 90-25 outputs asuccessive magnetization reversal detected signal of H level, forexample, when the data have a pattern in which a nonlinear bit shift(the time for which the drive current is supplied and the length of amagnetized region are not proportional) is easy to happen, i.e., apattern (010 or 101) in which the recording data have 2 successive bitsof magnetization reversal (a condition in which different logic levels(1 or 0) are adjacent to each other continues 2 successive times), andoutputs a successive magnetization reversal detected signal of L levelotherwise.

The selector switch 90-26 selects the constant C1 when the successivemagnetization reversal detected signal is of H level, for example, andselects the constant 0 when it is of L level, and supplies the selectedconstant to the adder 90-27. As a result, the selector switch 90-26outputs the constant C1 as a delay time T2 for compensating for anonlinear bit shift with respect to a pattern in which magnetizationreversal is produced successively, i.e., a pattern (010 or 101, asdescribed above) in which the nonlinear bit shift occurs.

The adder 90-27 adds the delay time T1 and the delay time T2, andsupplies the sum (T1+t2) as a delay time indicating signal to the pulsedelay circuit 90-30.

The pulse delay circuit 90-30 has its delay time controllable from theoutside thereof. For example, as shown in FIG. 52H, the pulse delaycircuit 90-30 delays the recording data (FIG. 52G) supplied from therecording data generator 90-16 by the time (T1+T2) indicated by thedelay time indicating signal supplied from the delay time controlcircuit 90-20, and delays a switching signal (FIG. 52D) supplied fromthe timing generator 90-15 to generate a write enable signal (active-lowsignal) as shown in FIG. 52F.

Specifically, as shown in FIG. 54, the pulse delay circuit 90-30comprises a variable delay circuit 90-31 having a delay time whoseperiod is equal to or less than one clock, a sequential circuit 90-32having a delay time in units of one clock, and a delay time distributor33 for dividing the delay time indicating signal from the delay timecontrol circuit 90-20 into a delay time in units of one clock and adelay time representing the remainder, and supplying them respectivelyto the sequential circuit 90-32 and the variable delay circuit 90-31.

The delay time distributor 33 divides the delay time indicating signalfrom the delay time control circuit 90-20 into a delay time in units ofone clock and a delay time representing the remainder, supplies thedelay time in units of one clock to the sequential circuit 90-32, andsupplies the delay time representing the remainder to the variable delaycircuit 90-31.

The sequential circuit 90-32 comprises a delay circuit operating insynchronism with the clock, and includes a counter 90-32a for countingthe clock. The counter 90-32a counts the clock for the delay times inunits of one clock for thereby generating a write enable signal shiftedin timing by delay times in units of one clock and an intermediateoutput of the recording data, based on the switching signal and therecording data.

The variable delay circuit 90-31 delays the data within the time of oneclock by the delay time representing the remainder, thus more accuratelydelaying the intermediate output of the recording data, and outputs thedelayed recording data.

The pulse delay circuit 90-30 supplies the write enable signal and thedelayed recording data to the recording amplifier 90-18. With such anarrangement, there is required one variable delay circuit 90-18 which isof a large circuit scale and is required to have a high time accuracy.Since the maximum delay time of the variable delay circuit 90-18 may beas long as one clock, the entire circuit scale thereof can be reduced,and its power consumption may be lowered.

The recording amplifier 90-18 controls the supply and cutoff of therecording current according to the write enable signal supplied from thepulse delay circuit 90-30, and reverses the recording current accordingto the recording data delayed by the pulse delay circuit 90-30.

The switching signal outputted from the timing generator 90-15 and therecording data outputted from the recording data generator 90-16 areheld in synchronism with the clock (FIG. 52C) generated by the clockgenerator 90-13 as shown in FIGS. 52D and 52G. As illustrated in FIG.52A, these signals correspond to positions on the data segments 90-2 asseen from the playback head 90-11a.

If the relative speed between the head 90-11 and the disk is representedby v, then there is a time difference T1=L/v between the data segments90-2 as seen from the playback head 90-11a as shown in FIG. 52A and thedata segments 90-2 as seen from the recording head 90-11b as shown inFIG. 52E. As shown in FIGS. 52F and 52H, the pulse delay circuit 90-30delays the switching signal and the recording data by the timedifference T1, generates a write enable signal and delayed recordingdata which correspond to positions on the data segments 90-2 as seenfrom the recording head 90-11b, and further delays the recording data bythe time T2 which compensates for the nonlinear bit shift.

As a result, it is possible to compensate for a phase deviation of data,to be recorded in the data segments 90-2, due to the distance L betweenthe playback head 90-11a and the recording head 90-11b in the directionin which they run with respect to the disk, and also to compensate for apositional deviation (nonlinear bit shift) of magnetization reversal dueto the pattern of the recording data. The data can now be recorded incorrect positions on the data segments 90-2.

Stated otherwise, the times at which the recording current starts andstops being supplied and the time at which the recording current isreversed are controlled by the pulse delay circuit 90-30 for therebyrecording data in correct positions on the data segments 90-2 withoutdepending on the position of the head 90-11 in the radial direction ofthe disk and the pattern of the data. In the playback mode, therefore,the reproduced signal is discriminated at the times (data-present-pointphase) of positive-going edges of the clock generated by the clockgenerator 90-13, so that the reproduced signal is referred to atpositions where data are present which are recorded on the data segments90-2, making it possible to reproduce data free of errors.

Another specific circuit arrangement of the delay time control circuit90-20 shown in FIG. 51 will be described below with reference to FIG.55. The delay time control circuit 90-20 shown in FIG. 55 comprisescascaded delay units 90-41a, 90-41b each for delaying the recording datafrom the recording data generator 90-16 by one clock, and a memory 90-42in which the delay time (T1+T2) has been stored in advance, using asreadout addresses the recording data delayed by the delay units 90-41a,90-41b and the head position information from the data demodulator90-14.

The recording data delayed by the delay units 90-41a, 90-41b and tracknumbers each of 8 bits are supplied as 11-bit readout addresses to thememory 90-42.

The memory 90-42 stores delay times corresponding to combinations ofpatterns of track numbers and recording data, and outputs a delay timeindicating signal according to the readout addresses.

Specifically, since the memory 90-42 stores appropriate delay times withrespect to all combinations of patterns of track numbers and recordingdata, the memory 90-42 can output nonlinear delay times, for example,with respect to positions of the head 90-11 in the radial direction ofthe disk, for controlling delay times in small increments.

The delay time control circuit shown in FIG. 55 may be combined with thedelay time control circuit shown in FIG. 53 such that rough delay timescan be calculated by the delay time control circuit shown in FIG. 53 andremaining fine time adjustment can be made by the delay time controlcircuit shown in FIG. 55, for thereby reducing the capacity of thememory 90-42.

As shown in FIG. 56, a magnetic layer, for example, is partly removed asby etching between data segments 90-52 which are regions to record dataon concentric magnetic tracks to form radial successive clock marks90-53 (the clock marks 20-11 shown in FIG. 2) for generating a clock anda timing compensating pattern 90-54 having a predetermined width, forexample, a width equal to the distance L between the playback head90-11a and the recording head 90-11b, on the magnetic disk 90-1 shown inFIG. 51. If the clock marks 90-53 and the timing compensating pattern90-54 are magnetized in one direction (the direction indicated by thearrows in FIG. 58A) by a direct current, then the magnetic disk deviceshown in FIG. 51 may have a time measuring circuit 90-60 for measuringthe time difference T1, rather than the delay time control circuit90-20, arranged as shown in FIG. 57.

The description of the circuits having the same functions as those ofthe circuits shown in FIG. 51 is omitted.

The timing generator 90-15 counts a clock to generate a time measuringwindow signal indicative of a period in which the playback head 90-11ascans the timing compensating pattern 90-54, as shown in FIG. 58C, andsupplies the time measuring window signal to the time measuring circuit90-60.

The time measuring circuit 90-60 measures a time T1 between the peaks oftwo isolated waveforms reproduced by leading and trailing edges of thetiming compensating pattern 90-54 in a period in which the timemeasuring window signal is of H level, as shown in FIG. 58B, andsupplies the time T1 as the delay time indicating signal to the pulsedelay circuit 90-30.

Since the duration L of the timing compensating pattern 90-54 isconstant regardless of the radius of the disk, the difference betweenthe times at which the leading and trailing edges thereof pass acrossthe playback head 90-11a is always equal to the difference T1 betweenthe times at which the playback head 90-11a and the recording head90-11b pass.

Specifically, the time difference between the peaks of the reproducedsignal corresponding to the timing compensating pattern 90-54 is thedelay time T1 to be supplied to the pulse delay circuit 90-30.

Therefore, the delay time T1 can be determined directly from the timingcompensating pattern 90-54 which is formed in advance on the magneticdisk 90-1. Inasmuch as calculating circuits including the adder 90-21,the multiplier 90-22, etc. shown in FIG. 53, and the memory 90-42 shownin FIG. 55 are dispensed with, the cost of the magnetic disk device canbe lowered.

In FIG. 56, each of the regions is illustrated linearly in the radialdirection of the disk for the sake of brevity. Actually, however, eachof the regions is formed along the path of angular movement of themagnetic head as shown in FIGS. 6 and 7.

As described above, the recording data are delayed based on thereproduced signal corresponding to the timing compensating pattern ofgiven width to compensating for a phase deviation of data, to berecorded on the magnetic disk 90-1, due to the distance between theplayback head 90-11a and the recording head 90-11b in the direction inwhich they run with respect to the disk. Therefore, data can be recordedin correct positions, and as a result, data free of errors can bereproduced.

In the manner described above, not only sector numbers and track numbersin the ID recording region 20-41H shown in FIG. 2, but also data on thedata recording region 20-41D can be recorded and reproduced by PRML.

The aspect of the casing 10-10 shown in FIG. 1 will be described belowwith reference to FIG. 59.

A lower casing 100-1 (40-51 in FIG. 19) made of aluminum or the like hasa hole 100-2 defined in a flat panel thereof for attachment of a spindlemotor 100-21. The lower casing 100-1 also includes a step extendingaround the hole 100-2, and a gasket 100-3 made of rubber or the like isplaced on the step for preventing air from leaking through a regionwhere the spindle motor 100-21 is attached. A shaft 100-4 is mounted onthe lower casing 100-1, and a ball bearing 100-6 (40-55 in FIG. 19)attached to an arm 100-5 (40-53 in FIG. 19) is mounted on the shaft100-4.

A voice coil 100-7 (40-63 in FIG. 19) is attached to one end of the arm100-5, and a slider (40-57 in FIG. 19) having a magnetic head isattached to the other end of the arm 100-5. The coil 100-7 and themagnetic head are supplied with a signal from a flexible printed-circuitboard 100-8 on which there is placed an IC 100-9 for processing signals.An end of the flexible printed-circuit board 100-8 extends out of thecasing. Magnets 100-11, 100-12 (62, 61 in FIG. 19) are mounted on thelower casing 100-1 such that the voice coil 100-7 is positioned betweenthe magnets 100-11, 100-12. The voice coil 100-7 and the magnets 100-11,100-12 jointly serve as a voice coil motor (50-5 in FIG. 21).

Two magnetic disks 100-23 (40-52 in FIG. 19, 50-1A, 50-1B in FIG. 21)are rotatably attached to the motor 100-21. The motor 100-21 has aflexible printed-circuit board 100-22 having an end extending out of thecasing for supplying a control signal to the motor 100-21 from anexternal source.

An upper casing 100-31 has steps 100-32, 100-33 on a right-hand sidethereof (as seen in FIG. 59). The ends of the flexible printed-circuitboards 100-8, 100-22 extend out of the casing through the steps 100-32,100-33. The upper casing 100-31 has a vent hole 100-34 defined in anupper panel (flat panel) thereof. A filter and a valve are mounted inthe vent hole 100-34 for introducing air, but blocking water.

FIGS. 60 and 61 schematically show assembled conditions of the lowercasing 100-1 and the upper casing 100-31. As show in FIGS. 60 and 61,the lower casing 100-1 comprises a plate-like member, and the uppercasing 100-31 is in the form of a box including a flat panel 100-31a anda side wall 100-31b. A gasket 100-41 is inserted between the lowercasing 100-1 and the upper casing 100-31 for preventing air fromentering the assembled and closed casing from around the flexibleprinted-circuit board 100-22 (or the flexible printed-circuit board100-8) that extends out of the casing.

More specifically, after the lower casing 100-1 and the upper casing100-31 have been assembled and closed, the interior of the casing isshielded from outside, and air can flow only through the vent hole100-34 in the flat panel 100-31a. Dust and dirt are prevented fromentering the casing. Since air flows in and out through the vent hole100-34, the air pressure in the casing is substantially equal to the airpressure outside of the casing.

The lower casing 100-1 and the upper casing 100-31 have a length of 100mm and a width of 70 mm. When the lower casing 100-1 and the uppercasing 100-31 are assembled together, their height is 15.0 mm if twomagnetic disks 100-23 are employed, and 12.7 mm if one magnetic disk100-23 is employed.

While the lower casing 100-1 is in the form of a plate and the uppercasing 100-31 is in the form of a box in this embodiment, the lowercasing 100-1 may be in the form of a box composed of a flat panel 100-1aand a side wall 100-1b, and the upper casing 100-31 may be in the formof a plate (flat panel 100-31c), as shown in FIGS. 62 and 63.

The casing shown in FIGS. 62 and 63 is characterized in that no holeother than the vent hole 100-34 is defined in the flat panel 100-31a.For a better understanding of this feature, FIG. 67 shows the shape of aconventional upper casing 100-31. As shown in FIG. 67, the conventionalupper casing 100-31 has holes 100-51, 100-52 and a recess 100-53. Therecess 100-53 is used to apply a label therein, and the hole 100-51 isused to insert a servo write head.

In the conventional magnetic disk device, if a servo signal such as ofan encoder were recorded on a magnetic disk before the magnetic disk isput in the casing, then since the magnetic disk would suffereccentricity due to pressure-induced deformation or an attachment errorat the time the magnetic disk is assembled, the positions where theservo signal is recorded as a positional signal would not correspondaccurately to positions where data are actually recorded. Therefore,accurate servo control could not be performed. In the conventionalmagnetic disk device, therefore, a servo signal is recorded on themagnetic disk after the magnetic disk is assembled in the casing.

Specifically, to record a servo signal on the magnetic disk assembled inthe casing, a recording magnetic head (servo write head) is insertedthrough the hole 100-51. Then, a servo signal is recorded on themagnetic disk by the head.

A mirror is installed through the hole 100-51 on an arm which is placedin the casing, and a laser beam from a laser length measuring unit isapplied to the mirror to accurately measure the position of the arm.While accurately measuring the position of the arm with the laser lengthmeasuring unit, the arm is moved successively in the radial direction ofthe magnetic disk. Servo data (encoder) are then recorded in a giventrack on the magnetic disk.

For example, when servo data are recorded in a radially outermost track,the servo data are recorded in quarters of the width of the track atpositions which are staggered by quarters in a direction perpendicularto the track. Therefore, a servo signal can be recorded on one track infour revolutions of the magnetic disk. In this manner, a rotary encoderis recorded on the radially outermost track on the magnetic disk.

After the servo data have been recorded on the magnetic disk, the holes100-51, 100-52 are closed off by given members, closing the casing.

On the magnetic disk according to the present invention, as describedabove, tracks and servo data are recorded in advance by impression atpositions as dedicated recording regions that are physically separatefrom other regions. Therefore, the positions where the tracks and servodata (formed positions) are recorded can be adjusted highly accuratelyusing a technique for finely controlling the position where the laserbeam is applied at the time the disk is formed. In this embodiment, itis only necessary to take into account eccentricity due to attachmenterrors.

According to this embodiment, as described above with reference to FIGS.34 and 35, eccentricity can accurately be controlled by adding an offsetsignal to a tracking error signal under feed-forward control. As aresult, servo patterns such as of the home index 100-73, the uniquepattern 20-72, the gray code 20-71, and the wobbled marks 20-12, 2013,and the clock marks 20-11, the sector numbers 20-41a, and the tracknumbers 20-41b1, 20-41b2 are impressed in advance on the magnetic disk.Even though the magnetic disk is subsequently assembled in the casing,data can accurately be recorded on and reproduced from the magneticdisk. As a consequence, it is not necessary to define a hole forrecording servo data in the casing in accordance with the presentinvention.

As no hole needs to be defined in the casing, the casing may be formedas a simple box or plate having a uniform height, and the mechanicalrigidity of the casing may be increased. Since mechanical resonance ofthe casing is thus suppressed, the head can be positioned highlyaccurately with respect to the magnetic disk.

Heretofore, since holes are defined in the casing, the magnetic diskdevice has had to be tested in a clean room to determine whether it isto be accepted or rejected. According to the present invention, however,since no hole is defined in the casing, the assembled magnetic diskdevice is not required to be handled in a clean room.

If the spindle motor 100-21 is of a lower profile, the hole 100-2 forattachment of the spindle motor 100-21 may be dispensed with.

The magnetic disk device according to the present invention can easilybe manufactured within a shortened period of time, and hence can bereduced in cost.

In the magnetic disk device of the present invention since the guardbands are impressed as concavities with respect to the tracks, the guardbands are not required to be wide for reducing crosstalk, and the trackpitch may be reduced to increase the recording capacity. Since thetracking marks, the track number indicating marks, or the clock marksare impressed as concavities and convexities along the path of angularmovement of the magnetic head, they can accurately be accessed even ifthe track pitch is small.

In the magnetic disk device according to another aspect of the presentinvention, a change corresponding to eccentricity of the disk-shapedmedium is measured, and recording or reproducing operation of themagnetic head is controlled according to a result of measurement.Therefore, accurate data can be recorded and reproduced even though thedisk-shaped medium on which the tracking marks, the track numberindicating marks, and the clock marks are recorded in advance issubsequently assembled into a casing.

In the magnetic disk device according to further aspect of the presentinvention, because the tracking marks, the track number indicatingmarks, and the clock marks are provided in 1000 combinations or less percircumference, the recording capacity is maintained, and the disk-shapedmedium can accurately be controlled.

Since the control signal recording region occupies 40% or less of onecircumference of the disk-shaped medium, the recording capacity ismaintained, and any disturbed motion of the magnetic head caused by theimpressed mark signals is held to a minimum, allowing data to berecorded and reproduced with accuracy.

Inasmuch as the disk-shaped medium comprises a resin or glass substrate,the magnetic disk device is lightweight. Because the surface accuracy ofthe disk-shaped medium can be made better, the distance between themagnetic head and the disk-shaped medium can be reduced, and hence themagnetic disk device can be reduced in size.

Since the recording head and the playback head are separate from eachother, data can be recorded and reproduced at high speed.

As the first marks are formed at positions radially displaced from thetracks, even though the recording head and the playback head areseparate from each other, the recording head can be aligned accuratelywith a track under tracking control when data are recorded.

Since a plurality of marks are provided, even when one of the markssuffers a dropout, data can be accessed with reference to another mark,and hence the safety is increased.

Because a positional change is measured from the tracking marks or thetrack number indicating marks, or a time change is measured from theclock marks, eccentricity of the disk-shaped medium can accurately bedetected.

Inasmuch as an eccentricity control quantity for correcting a positionaldeviation due to eccentricity of the magnetic head from the tracks iscalculated from the signal produced by reproducing the tracking marks,the track number indicating marks, or the clock marks, a positionaldeviation due to eccentricity can be corrected with accuracy.

The eccentricity control quantity which is calculated is stored, and thestored eccentricity control quantity is read out and added to a trackingcontrol signal to effect tracking control on the magnetic head.Therefore, reliable tracking control can be effected without increasingthe overall servo gain of the tracking control.

The time change is measured from the clock marks, and a time base of theclock signal is corrected according to the stored time change.Consequently, jitter caused by eccentricity or the like can besuppressed.

Since Viterbi decoding and CRC calculations are simultaneously carriedout, the reproduced signal can quickly be processed.

Since recording data are delayed according to the clock signal, a phasedeviation due to the distance between the playback head and therecording head and a nonlinear bit shift are corrected, and therecording data can be recorded in accurate positions.

Because recording operation is controlled according to the magnitude ofa positional deviation, erroneous operation can be suppressed at thetime an undue shock is applied to the magnetic disk device.

Since only a vent hole is defined in the casing, the time required tomanufacture the magnetic disk device is shortened, and the cost thereofis lowered.

The disk-shaped medium has a diameter of about 2.5, 1.8, or 1.3 inches.Consequently, the magnetic disk device can be small and light.

In the method of manufacturing the magnetic disk device according to thepresent invention, the disk-shaped medium is assembled in the casingafter the tracking marks, the track number indicating marks, and theclock marks have been formed and recorded on the disk-shaped medium. Asa result, the magnetic disk device can be completed quickly, and thecost thereof can be lowered.

What is claimed is:
 1. A magnetic disk device having:a disk-shapedmedium with a magnetic film formed on a surface for recording orreproducing information; a magnetic head for recording on andreproducing information from said disk-shaped medium; an arm supportingsaid magnetic head and angularly movable to move said magnetic head to apredetermined radial position on said disk-shaped medium; saiddisk-shaped medium has a data recording region and a control signalrecording region; said data recording region has concentric or spiraltracks formed therein, said tracks being impressed to have convexitiesas recording portions for recording data and concavities as guard bandsfor separating adjacent ones of said recording portions; and saidcontrol signal recording region having impressed concavities andconvexities representing tracking marks for effecting tracking controlon said magnetic head, track number indicating marks for identifyingsaid tracks, and clock marks dividing one circumference into equalintervals, at least one of the marks being formed along a path ofangular movement of said magnetic head; wherein said recordingsportions, said guard bands, and said control region convexities andconcavities all contain said magnetic film therein, and recording orreproducing operation of said magnetic head is controlled according to asignal produced by reproducing said tracking marks, said track numberindicating marks, or said clock marks.
 2. A magnetic disk deviceaccording to claim 1, wherein said tracking marks, said track numberindicating marks, and said clock marks are provided in 1000 combinationsor less per circumference.
 3. A magnetic disk device according to claim1 or 2, wherein said control signal recording region occupies 40% orless of one circumference of said disk-shaped medium.
 4. A magnetic diskdevice according to claim 1 or 2, wherein said magnetic head isseparated into a recording head for recording data and a playback headfor reproducing data.
 5. A magnetic disk device according to claim 4,wherein said tracking marks and said track number indicating marks havefirst marks used when data are recorded and second marks used when dataare reproduced, said second marks being disposed along substantialcenters of said tracks, and said first marks being disposed at positionsthat are displaced a predetermined distance radially from substantialcenters of said tracks.
 6. A magnetic disk device according to claim 5,wherein said tracking marks and said track number indicating markscomprise a plurality of marks having the same function.
 7. A magneticdisk device according to claim 1 or 2, wherein the signal produced byreproducing said track number indicating marks is subjected to CRCcalculations simultaneously while the signal is being Viterbi-decoded.8. A magnetic disk device according to claim 1 or 2, wherein a clocksignal is generated from the signal produced by reproducing said clockmarks, recording data are delayed according to said clock signal, andthe delayed recording data are recorded on said disk-shaped medium.
 9. Amagnetic disk device according to claim 1 or 2, further comprising:meansfor determining the magnitude of a relative positional deviation betweensaid magnetic head and said tracks as measured from said tracking marks,wherein recording operation on said disk-shaped medium is controlledaccording to a result of the determination of said deviation.
 10. Amagnetic disk device according to claim 1 or 2, wherein said disk-shapedmedium. said magnetic head, and said arm are housed in a closed casingcomprising an upper casing and a lower casing, each of said upper casingand said lower casing having a flat panel formed of continuous materialexcept for only a single pressure-regulating vent hole for adjusting thedifference between an air pressure in the closed casing and an airpressure outside of the closed casing.
 11. A magnetic disk deviceaccording to claim 1 or 2, wherein said disk-shaped medium has adiameter of about 2.5 inches.
 12. A magnetic disk device according toclaim 1 or 2, wherein said disk-shaped medium has a diameter of about1.8 inches.
 13. A magnetic disk device according to claim 1 or 2,wherein said disk-shaped medium has a diameter of about 1.3 inches. 14.A magnetic disk device according to claim 1, wherein said disk-shapedmedium comprises a resin or glass substrate.
 15. A method ofmanufacturing a magnetic disk device having a disk-shaped medium with amagnetic film formed on a surface for recording or reproducinginformation, and a magnetic head for recording on and reproducinginformation from said disk-shaped medium, comprising the stepsof:forming a data recording region and a control signal recording regionon said disk-shaped medium; forming concentric or spiral tracks in saiddata recording region, said tracks being impressed to have convexitiesas recording portions for recording data and concavities as guard bandsfor separating adjacent ones of said recording portions; formingimpressed concavities and convexities in said control signal recordingregion which represent at least tracking marks for effecting trackingcontrol of said magnetic head, track number indicating marks foridentifying said tracks, and clock marks dividing one circumference intoequal intervals, wherein said recording portions, said guard bands, andsaid control region convexities and concavities all contain saidmagnetic film therein; and assembling said disk-shaped medium and saidmagnetic head in a casing after said tracking marks, said track numberindicating marks, and said clock marks have been formed and recorded onthe disk-shaped medium.